On the other hand, it's their daughter's privacy. She surely wrote messages to people that she didn't want to share with her parents. And there might also be messages on this account that the parents don't want to find. People with psychological problems can write pretty dark stuff and she might also have talked about her parents in those messages. I'm not sure the parents will only get the closure they want, they might also dig up stuff, they later will wish they hadn't found.
So in the end, I'm not sure I agree with the judges decision. I think I share information with my parents the way I want to and definitely share other information with my friends in a group and 1on1 in messages. And I'm also sure I don't want my parents or another party not participating in some of those message groups to ever read that content.