Hello Krib. I hope your cat is going to be alright. If a cat loses weight then there probably is a problem. If your cat is running around and playing normally then I would think she is eating somewhere at some time. Is it strictly an indoor cat so that you know for a fact it isn't eating? If it goes out doors at all, it could be eating anything, wild caught, at the neighbors. It's hard to say. Just because you place food in front of a cat doesn't mean it's going to eat right then and right there

Cats do things on their schedule and not ours lol
If you're really worried and the cat seems to be acting oddly, then I suggest taking her to a vet as well.
Best wishes!
Ken