Puppy is bitting her feet and tail

When I used pedigree kibble and put some on the grass for her to find, she wouldn't really hunt for it - pretty much she couldn't find or smell it or just not interested.
Now with the Taste of the Wild, she immediately sniffed out all the kibble.
It was exciting.
Also, the puppy's poop had changed to soft solid material instead of diarrhea.
Additionally, the poop came out just after peeing, whereas before it would take an additional 20 minutes and it was also in the diarrhea form.

But, she still is nibbling on her rear paws and tail tip.

I am going to the vet tomorrow.

That sounds like great improvement! Give the itching some time to go away, it can take a few weeks in some instances.

Hang in there. I've been working on Sasha's itching since the day after we got her. Keep notes on what you do regarding food and her environment.