Then let them sue. It's not a concern of yours. If she wants to post fake pics let her do it, stop with your white knight exuses.
It's the internet, if it is available it is fair game. I'm sure you've illegally downloaded music before, you have no rights to that but it is done anyways. You cannot censor actions on the internet that is the beauty if it.
There are abilities to censor and certain culpability which comes with actions pertaining to the internet. However, at this point in time it's quite hard to censor but it has been done. But I doubt anyone would really sue over someone catfishing, that's absurd. However, people did sue over illegal music download sites.