answer:The only answer I can give you on this (aside from a general feel-good commendation for having her interests so close at heart) is “it depends”. That is, it does depend on her age, her “degree of deficit” (at least mentally) and whether she has a legal guardian or not. Does she need a guardian, if she’s of legal age to make her own carnal decisions? If she’s old enough and has the mental capacity for consent, and you can’t convince your parents (or a judge) otherwise, then it’s time to throw off her mooring lines, wish her well, hope for the best… and keep a lifeboat handy.