Girl AIM SN from facebook?

i think since you already sorta know her in real life then it would be okay to IM her. However, to help you save face (in case she does not want to get to know you better) how about the next time you two eat lunch/dinner together you just casually ask her if she has AOL or AIM or anything and ask for her screen name..if she lies and says no, then at least you havent wasted your time on her