Long ass reply so get a brew and get comfy.
No more trainers especially residential training 
That worries me to be honest I'd be really interested to find out more details and info about who and where you sent her for a month of 1-1 training. A random one for another time but in the meantime what I would do and suggest might be worthwhile.
Go easy on your dog. If she has been subject to different people expecting different things including a trainer whose techniques, methods and overall way of doing things you don't know and can't assume one way or another, you could well have a very confused and unsure dog.
Give her a break and go easy on yourself. You don't have the equivalent of Cujo running around killing small children and livestock you just have what sounds like a very typical retriever who maybe got lost and could use a few back to basics and simple refresher training.
All dogs push buttons, tests limits and act up no matter what breed or how they're trained and whatnot. Same way kids act up and work out which people are soft, which aren't and who won't put up or give in to a tantrum, dogs push buttons and will play us like fiddles too if they can.
Doesn't mean they're badly behaved or disobedient and need bringing in with a firm and harsh hand – it just means they're normal 
Retrievers are generally speaking known for being a) Lovely, good natured dogs and great family pets but b) Greedy fat bastards driven by food to the point they'll eat themselves to death if allowed and c) Obsessive and prone to resource guarding toys and tendency to nick and not let go of tennis balls.
A really common and typical problem owners have with the breed and actually one of the most straight forward things to resolve.
As a very general idea and from just the brief info here, this is what I would probably do for now
Walk her on a long-line and don't let her off at all just yet.
Get a harness and long-line or lead rope – whatever gives you confidence and better control for now and keep her securely fastened at all times for now.
She'll pull and argue and be annoying as hell initially because it's always worked for her until this point but each time she pulls, gets ahead or starts trying to drag you all over, stop dead on the spot and give one clear “SIT” then let her decide when and for how long this goes on.
Go no further and do nothing / say nothing else until she sits.
Don't yell, start repeating it or bribing her with food treats or anything else because she's already cottoned on and will probably expect that to work for her again.
No need for being harsh or doing anything other than giving her one clear word and letting her either do as you ask to get where she wants to be or not doing as you ask, fighting all the way and it serving absolutely no purpose anyway.
Dogs aren't daft.
There's much debate over the use of harnesses some trainers full-on, critical and keen to judge and jump on for people using them. For now you need only keep control and stop her slipping the lead and legging it . If that means a harness and rope instead of standard collar and lead – use one. It's not about what's right or wrong and whose method or technique is technically the best or anything else along those lines.
It's about you keeping hold of your dog, stopping her running away / keeping her safe and you feeling confident and in control.
Routines and exercise
Don't go mad or try to cram in a lot of exercise and activity there's no need and if anything she would probably be better off getting in a habit of just short, sweet walks on the lead. learning basic manners and adopting a nice steady routine.
An early morning walk just for 15-20 mins first thing and another during the day and again in the evening with access to outside for when she needs a pee and whatnot is more than enough.
Where possible try to make slight changes to your route so she's not anticipating everywhere you're going and getting overexcited and too ahead of herself.
You needn't run her ragged it can do more harm than good. For now the main aim is just getting her used to walking with and alongside you on a lead without dragging and pulling and barging everywhere.
Games and ways to make it fun and easier for her to learn
Dogs benefit more from brain games, mental stimulation and are better balanced overall when they have just a few short and sweet walks with time spent and training at home for simple games and activities at home.
Inside the house you can work on simple trick training or games that will get her brain going and help her to focus, stay switched on to you and follow your instruction.
Use what drives and motivates her so things like hiding little food treats inside a puzzle activity and encouraging her to find it is a good way to make her switch on and listen.
I find horse toys and stable boredom busters are better than most dog toys because they're made of better stuff and much more durable.
Letting go of toys and tennis balls on cue
Teaching her how to play hide and seek with a tennis ball or favourite toy is another simple but really effective way to use her brain, tap into what drives and motivates her and use it to your advantage.
Let her see and smell a tennis ball.
Hide it in an obvious place she sees you put it and then “Go find!” which of course if she sees makes it easier.
Step it up gradually and hide it under cushions in the same room or obvious place in the next room and when she goes to it – heaps of praise and “Yeee!!” or food treat whatever.
It's the ideal way to start work on teaching her to let go of whatever she's robbed and won't give up too. When dogs nick stuff belonging to other dogs out side, lot of people understandably grab and try to force the dog to let go. Retrievers are notorious for it but the simplest thing that often worst best is just don't pull and fight for it.
Literally hold the ball gently with your fingers, give one word whatever you use but for example “Drop it” “Let go” just once then wait.
The majority will automatically release and give it up without much fight or fuss. It's the pulling and resistance that makes them clamp down harder and decide to wrestle you for it most of the time.
Just hold and in a firm voice “Hey – drop it” and wait.
You can work on that from playing simple hide and seek in the house and each time she lets the ball go loads of “Yeeee good girl!” and a treat or whatever reward.
The aim is helping her learn to listen, focus, understand and follow your instruction. Few people even some pro-trainers really appreciate that dogs need to learn how to learn before they can learn.
We expect too much from dogs and give too little in terms of help with learning.
If and when she has mastered giving up a toy from the simple games inside the house and has learned to “drop” or “let go” you can even give her something to hold and carry whilst walking on the lead outside. One of mine used to love carrying a flying ring around with her and it would end up rank and dripping in saliva by the time we got home but she was never happier trotting around with that thing stuck in her mush.
My youngest dog came from a farmer who is without doubt one of the most successful, well known and highly respected sheepdog trainers and handlers in the country. He has training kennels people pay a fortune to have him train their dogs up for work, has won the international sheepdog dog trials twice and sells dogs he's trained for thousands.
The dog we took off him as a 1yr old fought constantly and wouldn't even walk to heel without constantly needing bringing back in and correcting and the poor lad was yelled at and yanked hard on the lead if he so much as blinked without being asked. He wasn't abused or neglected in any way but this farmer was just the sort that approached all dogs the same way. It was basically get bollocked if you get it wrong and if you don't get bollocked just join the dots and hope for the best.
The same day we brought him home it struck me how he didn't know “good boy” which when I said it made him stare at me vacantly with his head cocked to the side like I'd dropped from the sky. Taught him that good boy was “Yeee!! 
Best thing ever I'm super happy and you did it right!!” and with that he was switched on and has since lived to get a “good boy”
Like toddlers, when things are fun or rewarding – dogs want to engage, do more and make us happy and dogs like retrievers live and breathe to make us happy.
When it's not at all fun and everything comes with a harsh word, heavy hand and some form of punishment they don't' want to engage at all and to be honest, who would?
So yeah – long post and lots of info here I know but ultimately it's just a case of going back to basics.
Short sweet walks a few times a day on-lead at all times for now.
Praise what she does well even the slightest effort and failed attempts. Even a failed effort is an effort so give credit and praise where due.
Don't bribe or start getting frustrated and letting her wear you out. She'll try that's a 100% money back guarantee.
Lots of playing at home and using it to work on tweaking and getting that ball drive and obsessive streak working in your favour through a simple one word instruction to say “let go”
Keep it simple
Write a basic schedule for walks and indoor games and activities. Be clear and consistent and do not start letting things slip or getting lazy or she'll have you and work her way right back to being a toe-rag all over again.
I promise she will so much happier for it once you're in a routine and she has learned rules, boundaries, limits and is no longer constantly testing and pushing your limits and looking for trouble.
Before long you will be able to really enjoy having the best breed of dog there is to have as a family pet too.
Few links to toys, ideas for games and info about the breed that might help.
www.discount-equestrian.co.uk/stable-and-yard/horse-toys.html
www.goldenretrieverforum.com
www.bluecross.org.uk/pet-advice/how-stop-your-dog-pulling-lead
Also link to my favourite ever greedy bastard completely throwing his handler a deaf one and just inhaling treats as he goes. Fair play fella you can't knock him for effort