I think it’s the same why people stay in bad marriages. It’s hard for outsiders to understand. They must be getting something out of it.
It sounds quite strange that this grown up person wants to fully depend on others and wouldn’t even get a part time job but depending on others is easier than taking care of oneself. Her family and friends enable her by supporting her.
She perfected her game of helplessness. Some people live like this their whole life. Acting helpless and relying on others. Sad life if you ask me. But if others fall for it, not much we can do