Hmmmm, sounds like you have a problem. If she is your step sister then it's not really incest. However, if you do something with he that is something ou will have to live with without saying animation to a soul. If you feel it would bother you to do something with her and you can't handle that, then it's healthiest for you if you don't. Tell her straight up that you don't think you can handle that psychologically and that you want things to remain stable between the whole family without risk of complications that that can lead up to. If you want to be nice about it then let her know this but in a sincere way. It probly took a lot of guts on her side to approach you. Even then if you go to accept you may find out she is -blam!-ing with you. And that can only be bad. Edit: she may be serious. If you two are close then she may not want you to be an inexperienced person when you get with a girlfriend intimately. But I get the feeling she has trouble getting her own. Is she pretty? Edit 2- cuz this aint a game. Record in a diary with the dates on it the approaches she makes on you or any thine you feel like she is tempting you. It doesn't have to be a diary. Anything to back you up if she snitches. The second your parents get accusing about you just whip it ou an show them the proof. Her floor will tumble down the sinkhole