At the moment, her PR visa is still there. But her right to enter Australia has expired. If she obtains a whv, the PR visa will be cancelled entirely as the whv will replace it.
The ability for a 21 year old to then qualify for a PR visa in her own right would be very slim. So, if she went for a whv and then decided she wanted to stay, there is strong chance she wouldn't be able to.
Given her family is in Oz, I think she has a very sting chance of being granted the rrv. At the moment, many visa categories have seen processing times blow out. I would strongly urge patience.