Cats' personalities can change, but it's usually for the better unless they've been abused, which I'm sure is not your cat's problem. The only other thing I can guess is that bringing the other two kitties in has make her not as dependent on her people? It's not clear from your post if the other two kitties came into the home at the same time your kitty started to grow distant. I'm interested in hearing anyone else's theories and experiences.