Disrespectful Coworker

I am having a difficult time with a new co-worker, any suggestions are more than welcome. I work in a small office, for three lawyers; for five years it has been just us and we get along fabulously, with no issues at all. We hired a p/t assistant for one of the attorneys (she really does need the extra help) and this woman is awful to me. She is patronizing, condescending, invades my personal space, complains non-stop about stupid things (i.e. we don't have a magnetic staple remover), talks over me, especially with clients, and brings her drama to the office on a daily basis (she slept with her last boss). Most of this is done when no one else is around and that is most of the time. My confidence and my dignity have both taken a major hit and I am stressed and exhausted. I have finally had it after she made a comment to me about still having youth on her side. I had brought my concerns to my superiors after her first week when her unpleasant personality became obvious (there is agreement on this) yet nothing was done. I tried so hard to deal with her (sympathy, apathy, pushing back), but I finally told one of my bosses that I am seriously considering another job because I cannot take her unpleasantness and disrespect every day. I will give them credit, we had a meeting and she was confronted with her behavior toward me. However, how do I deal with her going forward? I don't think she is going to change, and it is apparent to me that her problem is with me. They have no intention of firing her (which I would have done after the first week), which makes me feel small and unimportant, even though I know my importance in that office. I have not dealt with a person so immature and self centered as she is since high school (and that's been a long time) and I cannot believe that she gets away with this behavior as an adult.