As someone who grew up with the internet and had to figure this out, I actually think you have an opportunity to have a good talk with your daughter here.

There will always, always be rude people out there. Right now she's encountering them in a video game, but odds are one day she'll be encountering them at work, while driving, at school, on vacation... sometimes she'll probably even be rude herself. Occasionally it might be someone overall decent taking their foul mood out on innocent bystanders. Occasionally it's someone who would find an excuse no matter what. Some people just aren't mature enough to handle mild inconvenience with grace.

At the end of the day, it's important to be able to say ask yourself "and why should I value YOUR opinion?" People lately have been getting this idea that respect is something you're entitled to, but it's not. Basic decency and human dignity are, but respect is different. Respect is something you earn. If someone clearly has a stick up their ass, you can disregard their opinion. Or you can see if there's anything remotely useful, take that, throw out the rest. There are too many people in the world who all hold conflicting opinions to take everything everyone says to heart all the time.

It helps to look at guides. It helps to say you're new at the beginning of fights. Even with that though, messing up sometimes is inevitable and encountering snotty people is inevitable.

Dealing with jerks in a game is a relatively safe way to do it, compared to at a job for example. Personally, I'd suggest your daughter not give up on an MMO she enjoys but have a plan for herself in the event that she encounters someone like that going forward.