They shouldn't be charged with anything.
The trouble with this so-called "psychological pain" is that different people react in different ways to things. Maybe another person would have just moved on with his life, rather than killing herself. Maybe somebody else would have killed herself after receiving a comment on myspace saying that she was ugly. It is preposterous that somebody should be liable for another person's responses to their nonthreatening, benign writing.
The girl had a choice whether to kill herself, and she chose to. Nobody tampered with her mental faculties in any way. She was not, for example, secretly given psychotropic medication. There was no crime here.