I know when our dogs were puppies, sometimes they just were to distracted with wanting to play they didn’t want to be “bothered” to use the bathroom. We would stay outside with them for a little while and continue to give them a “potty” command, we used “Go use the bathroom” and we would just repeat it over and over and then when they went we would make a big deal about it and immediately give them a treat to reinforce the good behavior.
If she is home alone a lot, it could just be needing more attention. Remember, puppies have A LOT of energy. 🙂
Good luck!
I would try chicken flavored puppy food. Otherwise, I would contact your local vet to be sure there is no underlying medical conditions.