I think you need to worry about yourself more and understand that everyone HANDLES things differently. Not EVERYONE who is abused physically or sexually grows up to have difficulty in their own personal relationships. Just because you did doesn't mean she did.
Some people also like to just put things behind them and live in the present.
Could you be using your sister as a distraction from your own issues with it? do you just want to talk about it so bad with someone who can relate and she's not willing to talk about it and that is bothering you? Maybe instead of trying to be your sister's therapist, you should get yourself a therapist to talk about this with.