Cockapoo pups are extremely persistent! I agree with the above posts. They are a mix of two intelligent working dogs. They need to be active and they need brain stimulation. I have had dogs of a few breeds, including border Collies. Even the Collies weren't as persistent with the mouthing as this fluffy piranha I have now.
Absolutely keep on with the training - recall and sit are the most important things your dog will learn. Once they have the concept of these two (your pup is too young to have full concept yet but give her another couple of weeks and she'll get it). Brain training and games tire them out. Stuffed kongs are brilliant when you need 10 minutes peace 😉
I very much doubt the yelp method works at the moment but if you are persistent it will click into place. When your pup was with her mum and she nipped her mum would yelp and ignore her. If you notice your pup playing with other pups their play will focus on nipping each other. You shouldn't try to stop a puppy from mouthing but it needs to learn bite inhibition - mouthing is fine unless it's painful.
Another thing I did when my pup wasn't getting the yelp method is smear some cream cheese over my fingers. Pup will lick the cheese. Lots if praise and a cue word for licking (I used gentle). My pup is 14 weeks old today and now when her mouthing gets a bit much I tell her gentle and she licks instead.
Don't underestimate your pups intelligence. She's still very young. With stimulation, Excercise and lots of patience- together with you working out strategies that's best for you both- she will pick it up in no time.
Like most things treat the behaviour you want and ignore the behaviour you don't want. I know, i know its virtually impossible to ignore needle sharp teeth persistently sinking into your flesh. You have to divert that energy into something more positive. Sit is a great diversion which will give your pup chance to calm down and you a chance to divert her attention to a tuggy toy for some structured play. As she grows your pup will go all out to please you ( and for the treat of course).
Puppies are exhausting! Keep on with the training and your pup will grow into a dog you can be proud of. Good Luck 🍀
Oh and please don't put your hands on her in an aggressive way e.g. smack her. Your puppy needs to see your hands as a positive thing.
Apoplogies if your pup is a boy btw. I use she as mine is a girl.