If you run away with my sister, I would at least hope that it occurred with the consent of my sister. If yes, then of course I would not have a right to decide for her and to intervene for as long as she is happy with you.
However, if it is forced in any manner then I would consider following the law and build a legal case on you for abduction. Nevertheless, I will consider it my right to investigate what you motives are at the end and might even use the help of some investigation agency if the need may arise.