Wow, I'm really surprised at the lack of comment about her upbringing. I don't know how in the hell her mother even had custody to begin with, given the circumstances. And I don't know how long she has been around these people, who are nothing short of bad role models. But, I do know this. If what you said is true about her uncle, mom and aunt, and she's been exposed to that for long enough, that WILL be the only way she knows how to behave. She's not a 'normal' 13 year old, regardless of it being 1955 or 2010. She's been exposed to abuse. She's had totally ****ed up role models, and I find it sad that so many people seem to not even realize how much of an impact all of these facts can and do have on her. The facts are that her grades are slipping and she's lost interest in things that she used to enjoy. Is it the boyfriend, or the familial issues? Or something else? Doesn't matter. The red flags are there; something is definitely going on. I would also like to mention that I find it strange that she would tell you about her diary and that everything is in it. I'm not sure what that means, but obviously, whatever is going on, she's not trying very hard to hide it from you. I wouldn't go through her ****, though. As others have said, I'd just talk to her about it, while you're calm, and make it clear that your concerns are out of love, and that you are not angry. The more you two talk and get to 'know' each other, the more forthright she'll be with you in the future.