It technically doesn't matter. It was obviously someone higher in the chain of command than she, so as far as she was concerned this person had the authority. If she had been taking too much time, then she should have been called and informed she needed to return to work. She said she took her vacation time plus 30 days. Now I know that people grieve differently, but it does seem a little excessive. But Disney really should have called her and explained to her that she needed to return to work as opposed to waiting until she returned.
It absolutely matters. Disney is a large company so I have no doubt that they have employee handbooks that they give to all their new employees that those employees then sign for saying they have received, read and understood all of the company policies and that their failure to follow them can lead to their termination.
So if the women was in violation of these policies (which, just judging from the amount of time she was gone I would guess she probably was) then they had every right to fire her.
Again, we don't know the whole story. For all we know Disney was in constant communication with her. Honestly though, they have no obligation beg people to report to work or resonably communicate with them.