Puppy Not Eating - Advice?

Following on from my previous post, I have a 14 week cockapoo puppy who we’ve had now for a month and since getting her has not had a full day of eating her food.

We’ve tried mixing wet and the dry food she was on with her breeder (Purina Pro Plan Puppy) and she’ll either suck the wet food off and not eat the dry or not touch at all.

We’ve spoken to the vet who confirmed she was underweight and they provided puree for a brief period to mix in with dry food which worked briefly, but couldn’t continue to use it as it’s meant for dogs following surgery to regain appetite. We also split her three meal times to five as advised to the vet which had no effect.

We’ve tried new food (Burns) which she did seem to like but has now stopped eating and won’t eat either made soft with warm water or mixed with jelly.

She’ll happily take treats (we don’t feed her a lot of them), but just will not eat!

We’re at our wits end as we’ve spent SO MUCH money on food etc and nothing seems to work.

Any advice or suggestions or experience welcomed as we’re finding this really difficult.