Unbelievable Rudeness!

[Fredco191]

As a fellow kid playing an MMO. This is just something she’ll have to get used to.

[Durandallwyn]

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

[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.

[Xebric]

As a fellow kid playing an MMO. This is just something she’ll have to get used to.

This for sure. I'm not advocating for rude people, but what will happen when this happens at school, at work, or in her personal life? At some point she'll have to either suck it up or stand up for herself. The world is not going to change solely based on the needs of one person, but she can learn ways off dealing with rude people like that. My personal go-to is to just take a break from the game, cool off with Pac-Man or Dig Dug, and possibly report the person(s) for what they were doing if they were excessively rude. Yes, it's unfair that her fun time was ruined by some rude people on the internet, but dwelling and obsessing on it doesn't hurt those rude players. Moving on and dusting the incident off your shoulders and not letting it weigh you down is the best way to go about it in my experience. Also friends / family for consistent groups makes for pretty regular fun times instead of random groups.