I started to play Diablo 1 online that I was 3. Following up Diablo 2, WoW, Dofus and many other online games.
Not a typo. I was literally three years old when i started to play computer games and online since I used to play with my grand-dad, still remember he helping me giving me Enigmas and other runewords in diablo 2 \o/.

Thing is, online has always been filled with people that feels free to bring down others because its just behind a screen, so they feel strong to talk like that. I'm sorry for your daughter and yes I do think the "cyberbullies" are a bad thing, but this ain't a case of cyberbullism, he just blamed her for an her mistake. Its not a matter of confidence but skills. I started to play very early, especially in WoW i was being blamed every so often, but the right approach i thought and i still think is to take it positively and step back and say "Yes i didn't do a good job, next time i'll get it". I'm really sorry for your daughter getting offended but that's not a case of cyberbullism, thats just someone making a rude comment, getting blamed and pointed in MMO's happens everyday to everyone of us, from having a bad day to being inexperienced and many other causes that other person that had a bit of a bad day or just likes to be a rude prick can't know, making one comment at a random does not qualify for bullying you out of it.
That being said, hope your daughter gets harder shell, online has never been a good place for a kid I best of all know it.