The best thing to do is to confront your roommate and tell her that you are not a lesbian, and that although you appreciate her liking you- you cannot be attracted to women (like she may not be attracted to men). I believe that a little friendly talk would not hurt. Moreover, it may be just in your mind - ie. her staring at you...etc. Just make sure its not a fragment of your imagination. Lesbians are not attracted to ALL women. So just because you are a girl, and she is a lesbian, there doesnt have to be an immediate feeling of "she wants me."....If all this doesnt work, and you are certain that she continues to pursue you - then - AVOID her AS MUCH AS POSSIBLE. IGNORE. MAKE HER BELIEVE THAT SHE DOES NOT EXIST IN YOUR LIL WORLD. :)