I am still in the process of learning and cannot say what high risk or low risk factors do what but you can find information at the Center for Disease control that may answer your questions. Good luck to you and your sister.
Low risk HPV causes warts. High risk HPV can lead to cancer if undetected and/or untreated. If a woman is told she has high risk HPV it is the latter catagory. That means that she either will have some more follow up appointments/procedures OR she will have to be sure she gets her annual exams on schedule and never miss them.