it sounds like you introduced her immediately to your other cats as soon as you brought her home. it's possible that what she really needs for a while first is to be isolated from the other cats, so she feels she has her own space and feels safe. if she was bullied by other cats at the shelter and she already feels bullied at home now, then that could be why she has no appetite.
also, are you feeding her the same stuff the shelter was feeding her? a change in food might be a little shocking to her. but I assume since you already have cat experience, you've stuck to the same food. if that's not working, try anything! more tasty foods!
what was her history at the shelter? did she have very little appetite there already, too? if she was eating good and starting to gain weight at least, find out everything you can about what they were doing and try to match it at least for a while till she gets her bearings.
just a few thoughts.
Kitty, Lucy, and my sweet Angel forever in my heart.