Puppy doesn’t eat much

Hi! My 7 month old puppy didn’t gain any weight in the past month – she was 10.14 pounds a month ago and 10.4 pounds this week. She eats Purina puppy chicken and rice, which she’s been eating since she came home, and technically gets a 1/2 cup in the morning, 1/3 cup at lunch and 1/2 cup scoop at night – but realistically she probably only eats 1/2-2/3 a cup each day between those meals and leaves a lot untouched. I wanted to have set mealtimes but have instead been pretty much free feeding because I’d rather she eat SOMETHING. She goes crazy for treats, seems to drink enough water, pees and poops normally. She’s on the lean side but super fluffy so hard to tell exactly how skinny. Seeing the vet soon so will ask them as well, but has anyone else experienced similar? Should I just trust her to eat what she needs or is there cause for concern?