My dd is 14 and last year we discovered she was looking at porn online. Thankfully, it wasn't chatroom stuff, more that she was looking up pics and vids, mostly anime stuff.
First, DH and I did NOT freak out. What really surprised me was that she was using the family computer, she doesn't have her own. And she knows that I can and do use it at any time. As computer savy as she is, she apparently didn't know how to clear the history. Anyway, when I checked the history and discovered it, I closed everything out and when DH came home and DD was out at a friend's, I showed him and we talked about it first.
The thing that really struck ME and that made me really assess the whole thing somewhat objectively was that the first thing DH said was that had it been a son instead of a daughter, he wouldn't have thought it was a big deal. So we had to have a big discussion about double standards and the fact that he and I both look at porn and enjoy it together and that we both found and pilfered our parents stashes when we were her age. And we had to talk about what we ACTUALLY thought was wrong with what she was doing.
We realized it wasn't so much the fact that she was looking for porn, it was that there was a lot of false stuff in porn and we didn't want her to get the wrong idea from anything. And the fact that porn sites are full of viruses and malware, which resulted in her having filled up the computer with that crap in no time.
So, we sat down and talked with her about exactly that. We talked to her about why she was looking, told her that it was ok to be curious, but that what she sees online is as much acting as any other movie, that it's as fake as Star Wars or Titanic. If she wanted to get any questions answered, that it was best to come to us, we would give her the most honest answers we could. We also told her she could not look for porn online for the more practical reason of it filling up the computer with viruses and stuff. We actually ended up having to crash the computer and reboot it from scratch, which meant she lost some of her creative stuff that she had saved. But I know she learned that lesson.
We also talked about how if she was having "those urges" that masterbation was ok, but that it was something best done in private in her own room. It's been my experience with her and with my nieces and nephews that for the most part, little girls are less "exploratory" in that respect than little boys are and so we hadn't had the opportunity to really talk much about that sort of thing when she was little. When she and I had "the talk" we discussed it some, so she knew what DH and I were talking about, but we wanted to reassure her that it was ok to do, just not in a main room, on the family computer.
As far as books......I am ok if the books she reads are a little racy. She is WAY into anime and while most of the manga she reads are "age appropriate" I am also aware that some might be a smidge on the racy side. They aren't Fabio romance novels, but I think they contain enough to satisify the curiosity and urges, in a much safer manner, IMO. I feel like she's much more able to grasp the fictional aspects of the stories as well, in book form, than in "live action" forms, if that makes sense. It's much easier for me to read about a bloody gory battle for example, than to watch Gladiator on tv, I feel like sexual references are the same way.
NOW, having said that, internet safety, in regards to chatrooms and such are a whole seperate issue, IMO. I don't care if people are talking about sex or soccer, it's never safe to willy nilly hand out full names and addresses and such. We have always drilled internet safety into her head and I regularly logged into and gained membership to any website I found her on. And I made her well aware that I was "following" her around online, by randomly brining up things she discussed on those message boards and such. And if I ever became seriously concerned that she was sharing personally indentifiable information, OR if I thought her friends (IRL friends who she also associates with online) were sharing her stuff, she would absolutey lose privlidges online AND with those friends. And if became some sort of problem, I would have no problem installing blocker programs, just like workplaces have.
As far as her phone....we have internet blocked on all our phones. We pay very basic rates for financial reasons which means that net surfing is EXPENSIVE. And therefor not allowed, so it's blocked on all of our phones to prevent accidental useage. And texts...she pays for all her texts. She has a "job" at a family business, so she earns her own money, which means she pays for some privlidges, texting is one. Bonus, it keeps her in check, she set her own limit of $2 worth (which at $0.20 a text is about 10 messages a month.) And at this point, she isn't even using that.
SO, that's a long post, but I thought I would share how we handled the porn situation when we ran across it. I am not sure how well any of it might work for you if she has other behavioral or mental issues as well.