My roommate is borderline psychotic and is harcore stalking this guy who has no clue. What should I do?

Some people do the occasional stalking of someone's facebook profile just to find out more about them. However, my roommate checks this guy's tweets daily, finds out where he'll be, and has shown up on multiple occassions so she can see/watch him (not even go up and introduce herself or try to have a normal conversation). She isn't a shy person, in fact she won't stop talking most of the time, so her behavior is really creeping me out. She thinks it's necessary to tell me the things she finds out about him so now (incidentally) I know like everything about him--I've become a "stalker by association". I know it would be really mean to rat her out, but she needs to either talk to him/stop stalking him or get herself a boyfriend asap. Do you have any advice???