It's not THAT revealing, true, it was more intended as a warning for the future to be honest, and a more general one, not just for her. Many young girls (13-16 for example) put 'bragging' pictures of themselves up on sites like Facebook, without understanding the possible consequences. Coupled with poor privacy settings (like a fully public profile), this is highly inadvisable. You never know where those picture CAN end up, or who may see them.
In terms of facebook, it's well worth knowing that any picture you upload there is the properly of Facebook, and they can use it for whatever they fancy, including advertising. The chance of that happening probably isn't very high, but it can happen, and it has. I just wish people were a bit more careful, in general.