She's got what some musicians call "First Fame" when everyone cares what you think and you think everything you say is very important and some divine force is talking through you and "no one ever said and did what I'm doing." It comes from not going to school with other kids, being self absorbed, getting famous when you're really young, and thinking you're entitled to all the fame.
Her brother is more grounded and seems nicer - he's actually said, many times, "we're really, really lucky and very, very privilaged."