It could have something to do with the change in her routine as that can be stressful for them, but I will say that I have noticed my squirrels eating much less at certain times of the year. My 4 year old boy goes through spells where he hardly eat anything at all and it always worries me. I even have cut out his treats and he still just won't eat much. And then other times he eats everything in sight.
I really think it has something to do with the seasons even though they are indoors. I have noticed a definite pattern with the times of year he eats less. As long as she's showing no other signs of illness, I would say keep offering her plenty of healthy food and veggies and really limit treats until you see she's eating the healthly stuff well again.