Though your pass will have your name on it, it is very doable. Using a one day pass means that person has to use their fingers to scan and your sister can do that because the pass is no good after it is used the first day. My daughter used both hers and her friends while in WDW in September. The worse thing that could happen is that they might ask her for an ID, highly unlikely, and if she doesn't have one, they certainly are not going to stop her on a one day pass. I wouldn't worry about it, and have your sister sign the back of the card--your name.