Hey when I was 5 I had a 7 year old ask me for sex, it was my mothers friends son and whenever we stayed over he would lie in bed and ask me to have sex with him over and over and over until he fell asleep, and yes, I nearly caved in, to the point I had my clothes off. I still don't know what to make of it. A few years later my mother forced me to call his mother myself to tell her what he'd done, I was in tears about it because I didn't want to call (I was maybe 9 years old), thank God she didn't answer the phone.
So I think while something needs to be done about this you need to be careful how. Reporting her on Facebook I think is okay, you just go to her profile and report it from there and give an explanation.
I do also agree that perhaps something may have happened to her, but her behaviour isn't proof that something is, she could just be wanting the attention. I went to high school with a girl (who I am friends with now) who was extremely promiscuous, she had a reputation as a slut and quite frankly, it IS really difficult to argue otherwise.
But I try and have empathy about it instead of be nasty like other people. To me it is as though she needs the attention. Not to be nasty to her at all (and I do feel bad for saying it), but she is largely overweight and not the most attractive person. BUT, guys will her she is, because they know all they need to do is talk it up with her and make her feel good about herself, especially with the amount of crap she got at school, and possibly elsewhere.
I think she NEEDS that attention and is willing to have sex with just about anyone because it's the only time someone tells her how great and attractive she is. She's just lost all respect for herself.
She has even made me feel rather crap about myself, she always talks about people from school, she asks if I have seen there photos on Facebook, how AMAZING they look now, they are SO beautiful now, that I have to look at them. But then when it comes to me she just says 'oh you just look the same as you always have'. Even when I tried to make myself look nice before I see her- nothing. As if I haven't had enough image problems as it is. I have to listen to her talk about how attractive these people are, some being amazingly beautiful, and others being, well, I have no idea what she is talking about.

I have another friend who is a 'model' and posts pictures of herself in tiny outfits, even in a bikini while she was 7 months pregnant. And her outfits don't really suit her body type. But because she's got it all hanging out people tell her (the majority guys) that she is so good looking. Well I can't wear outfits like that, so again it makes me feel like crap. And some of the comments these guys make, it's just wrong. I've deleted some guys from my Facebook account (I haven't been on there in months though) because half their wall comments are about sex, one guy I used to go to school with as a kid kept posting really derogatory comments about women so that they looked cheap and only good for one thing.

So of course now I have started to obsess about my appearance again and can't stand to look in the mirror. I've even been thinking of surgery.
My point is, this is the pressure a lot of younger people go through these days. They need to be TOLD, and they start to crave it. I hate people commenting on my appearance, but the same time I don't need it to be pointed out to me that I'm not that attractive.
This girl may need that attention, she might be putting bikini pictures of herself up because she 'can'. She has the body for it, and there is so much competition to be more attractive and thin. Girls look at other girls. Girls compare themselves to other girls. Like I mentioned in an earlier post my friends used to sit there and compare ME to other thin girls they knew and work out who was thinner and therefore more attractive.

The only problem with reporting this girls photos is that they may actually delete her entire account.