This is going to be the most important post in this thread so far. Please read it. This is going to be one of the only serious posts I ever make on this board (did you know that my brother is a fighter pilot?)
Whatever you get her, make sure that it doesn't have a built-in webcam.
If you go down the webcam route, you will regret it. End of story. Without a webcam, not only will your daughter have less pressure on her from her peers, she will also be (somewhat) insulated from temporary lapses in judgment.
Lots of folks on here know that I work for the Federal Government, every week, we have at least one predator picked up. Please don't expose your daughter to the unnecessary risks that a webcam entails.
If you're asking this question, I assume you've already purchased her a cell phone. Don't tell yourself "well, if she's going to do *that,* then her phone is just as much of a risk." That is wrong. There are so many more avenues for attack/persuasion via the Internet than over a phone. That isn't to say that a cell phone in a teen girl's hands isn't one of the worst things ever - because it is. But a fully functional laptop with a webcam on it isn't going to happen for my Daughter before she's 18, a desktop is going to be fine for her.
Worst case scenario, you get a tech guy to lock the shit out of that webcam.