I'm in a couple ana kik groups and go on Omegle to chat about eating disorders/anorexia sometimes. Even though I'm 20 and not as impressionable (at least I hope so anyway), I almost got tricked by a predator. It's pretty common too and it makes me sad when a lot of the girls in the kik groups constantly looking for ana coaches when it's now clear to me how their sole purpose is to exploit the vulnerable. So I think it's wonderful that you're thoughtful about the well-being of the girl and I do hope you could help be a positive influence to her.

Also, I don't think you can give her an ED by talking about disordered behavior. There are so many underlying causes - genetics, family, negative coping skills, trauma, so on. The fact that's she's seeking support at her age probably means she's been through some stuff. There also isn't conclusive evidence to suggest that pro-ana has negative effects on people who talk about it. According to one research paper:

pro-anorexics displayed more positive emotions, less anxiety, a lower degree of cognitive reflection, and lower levels of self-directed attention than did recovering anorexics. Pro-anorexics were also more focused on the present and less on the past. Finally, pro-anorexics were more preoccupied with eating and less with school-related issues and death.