My dog was a nightmare at 18 months
Chewing things up, mouthing, humping, reactive to other dogs in an excited way (frustrated greeter), loads of energy. Our kids are older and can help and Dh helped (although reluctantly) but it was shit. A year later it's much better and I am glad we didn't give him back to the rescue. I often thought of it but would have been ashamed to quit.
If you put some big effort in. DP has to as well. For 6 months things will be better and you will have a lovely dog.
You could use her food to much better effect
100% start making her work for it.
Mine has a Kong, a Kong Wobbler and a snuffle mat to make meals last longer and we keep some back from his food allowance to reward him during the day
To get any of that he must sit, wait, make eye contact and not jump up to get any food. He cottons on very fast where food is involved.
Also walks. In order to go out he must sit, wait not jump up or bark. I don't open the door until he does those and if he moves or barks the door shuts. Again he got that super quick in one session because he really really wants to go out.
Trainer suggested don't expect too much all at once. First thing out of the gate he's super excited and no training will register so try to get somewhere quick that he can run a bit. Ours seems much calmer after he's had a poo! Then do the loose lead walk training on the way home. As it gets more embedded you extend it.
On walks I take a treat pouch with chicken and sausage at all times and to start with would reward just him checking in and paying attention to me. He knows stop, heel (come back to my side), watch me and I can now get him to walk calmly past most things although cats and motorbikes are still an issue. Also bought Total Recall and worked through that. He's not 100%. Still buggers off like a twat after other dogs occasionally but much less and I can usually pre-empt him as I can read him better now.
He has a Ruffwear harness and a longline and that has been a godsend once we both got used to it. It means he can have some freedom to sniff about but still be on lead. DH also uses an extender lead but I never do. I much prefer the longline. With the longline you can drop it to let them run and still have a bit more chance of getting them back by stepping on it. I used to do that quite often.
Once you know they are fed and had a good walk then you tell yourself their needs are met and you ignore pestering and reward them for settling down. You wait for them to get bored and go lie down and then you lob a bit of kibble. It takes a while but with a combo of no reward for pestering, reward for lying down calmly and routine that's how my dog learnt to have rest periods. Routine is so helpful as dogs go off cues a lot. If mine sees me sit down at my laptop he goes straight to bed now as he knows he won't get attention when I am working.
I would recommend a new trainer
We've had at least 4! One I binned off for wanting is to get an ecollar, one was classes in a village hall which he dicked around and we didn't get far, the two best ones were 1:1 classes outside or in a dedicated arena with a guy who does gun dog for all and man trailing (I cried on him once I was so pissed off with dog) and a lady who does scent work. Those were loads more successful. Partly just he's a big dog and he needed more space. Initially I thought why would I train him to do silly stuff when I just want him to behave but in fact it's working on your bond, doing something positive together so you can feel good about her again and it's transferable stuff mostly impulse control and paying attention to me. It's also true that it tires them more to use their brain. Ddog can't really manage a full 1hr class. He often gives up and lies down before the end and then he sleeps deeply.
He has 2x45 min walks a day but shared between me, DH and teen DD. At least one with some off lead time.
7am wake up straight out for walk
8/8.30 breakfast
Lie down til lunch time
12/1pm we have lunch, he often has a frozen Kong or a chew and we always do some training games. He enjoys a sequence of basic stuff for a reward (sit, down, paw, touch nose, spin, go to place, stay, walk to heel).
1-3.30/4 Lie down till kids back from school
4pm plays with the kids ball, tuggy (loves his TuffENuff fleecy toy so much we have 3), hide and seek kids or toys
6pm walk usually more of an on lead sniffy one
7pm dinner and hang around hoping to 'help'/ get scraps when I am cooking or washing up
8/9pm go and settle down in living room and hope to get invited on the sofa
11pm goes to bed downstairs
I used to get pissed off that so much is management of the environment etc (why can't he just not do it?!) but it is. We got a box for shoes, put remotes on a high shelf, never leave any food on counter tops and we got an outside mailbox and never let him in the living room unsupervised in the daytime (he barks out if the window). Mostly he no longer does any of that stuff. He no longer got any reward for it so he stopped basically.
Our trainer used to talk about paying the dog for their work so any behaviour you like to see you pay in food or fun and any you don't you ignore.
DH is still a bit prone to shout at the dog for bad behaviour but really it is pointless as dog has no clue what you mean and possibly even thinks it's good that he's getting attention. This is why dog demand barks at DH and not at me...
Basically this is a tough difficult stage but she can be a good dog once you get out the other side of this. Sit down with DH and make a plan of attack. Divide up walks. Agree on a routine and rules for everyone to be consistent with and look into a new trainer.