My fiance's sister is a sex addict?

She's 15. She started liking sexual things at I'd say 11 years old.

I know this because on one of her accounts she linked to me, I saw another account in her profile, clicked on it out of curiosity and it was a blog about sex that she wrote from a few years ago which means, she was 11 when she wrote it.

I then saw a link to her 'list' of recommended sexual movies that you 'should' watch. They were all adult-rated and were all explicit and showed lots of full sex scenes.

She even rated two movies and said how amazing it is and that it's a great reference to what sex is like/'tips' again on how to penetrate a women.

This deeply disturbed me and I thought it stopped there until I found a link to a new blog from just a year ago when she was 14. She talks about how she can't wait to lose her virginity and that the second she loses weight, she's going to have sex with the first guy who asks her out. This is a direct line, "I wish I could have had sex years ago but I haven't had a boyfriend yet because I've been fat so I will just wait until I find one and then have sex with him.". She then discusses the type of penis she prefers and how she would turn a guy away if he wasn't 'adequately endowed'. She also LIES about her age and says in the blog she's 19 and posts a photo of herself. So I know it's her, I know she's lying. Her friend posted a comment, so I got curious, clicked on her friend's profile and there's a photo of her friend and her and there are several photos of her friend with tape over her nipples and a hand over her female part lying on a bed...her friend is 14.

IIN? Should I be worried? This is a girl who will be my family soon and she's family-oriented more than friends-oriented so I can trust I'll be seeing a lot of her when me and my guy tie the knot. BTW this girl is not super outgoing with me, she's actually really quiet and barely speaks in front of me so what she posts about doesn't match her.