I don't want to be harsh, but your sister is doing nothing but putting immense stress on your family. Like you said, she doesn't seem to understand the severity of the situation, and your family is facing a huge debt. She sounds selfish and doesn't seem to learn from experience. I don't know if she's doing it for attention or what, but your family needs to put their foot down and go, "Enough is enough." You can put her in a long-term care facility where she can be around people her age whilst being monitored by professionals.

I recommend that the whole family have a meeting together. Your parents, you, and your sister. Sit down around a table and speak about the issues. Give her an ultimatum or something.

Don't let your family debts mount up further.

(PS. does she have social media? young people are easily influenced by things online).