Aw geez, crazy vet!!!!

If you disturb the "nest" too much, Bella will move the babies. Since you know where they are, you feel it is a secure place, and she is coming to you for food, maybe just let things be until the kittens are mobile. If she moves the little ones, you won't know where, may not be able to find them, and it may not be a secure a spot.

Buy the highest quality food you can get for her. Best!