I would most definitely give your vet a call. It is quite possible that she is ill, and the agressiveness is her way of "acting out" in order to get your attention. I often wish my dogs could talk and tell me what's wrong when they aren't well. This just seems so very sudden, that I am concerned that she really is ill, and I don't think I would wait much longer.

Hope it all works out. Rat terriers are so adorable, and it was good of you to adopt her. I'm a four-chihuahua mom myself, so I love all of the little ones.

Anne