It's probably not a good idea to post pictures on the internet at all. :S

That picture that is hosted on facebook can probably be tracked through search engines. Now imagine that her name becomes linked to this photo and this photo is now linked to this post. And ,say, one day she goes to find a job and the company starts searching her name on the internet. If they find out that she might be lacking a self-confidence, do you think that would give her advantage over competition ?

Also, some people might search for random photos on the internet to use as avatars for whatever reason. (use it as a hook to bring traffic, etc).

The worst of all, someone will photoshop her face into another photo and it somehow turns into viral photo that spreads over the internet like a wild fire. Will that help her?

My advice to you: you support her as much as possible. Go outside with her, make her meet ,real life, people. That's how she will gain confidence, not by sitting at home surfing the web, reading posts written by strangers. Ooh and sorry if I sound like an ***..