Unbelievable Rudeness!

[NessaWyvern]

Maybe playing single player games without others is better as to avoid cyber bullying.

Yeah, it can be tough as a kid on MMOs sometimes, I started playing MMOs when I was 12, and I got cyberbullied back then.
Unlike RL bulling though, at least you can blacklist so you never have to read that person's vitriol again.
Perhaps help teach her about how to deal with these situations online, like the report and blacklist functions. Continue to supervise her while she is playing, and if someone says something bad about her, tell her all the ways she's good at the game.
If that still doesn't work out, then I suggest waiting a few years, as people have said, this game is rated 16+

Perhaps only let her run dungeons with you in her party, and bring along trusted friends to help her, to try to build a friendly atmosphere for her.
You could disable her Party chat, and tell her what they say instead, so if there's anything nasty, she won't know about it unless you tell her.