Echolalia

If you aren't really interested in the crazy one I say just don't go there...don't mess with crazy people (and she does sound a bit nutty). Go for her friend, ask her out directly and say that you are into her and not the other one (perhaps you can ask some of your mutual friends to "ask around" and see if the crazy one tried to sabotage anything). If nothing happens of asking her out, just stay away from the crazies...