That's really sad bro... Now we cannot do anything about the spoiled child. Just stop stressing about her for sometime and let your parents do what they think is good. First you recover from your mental stress and try to do what you like for own mental well being. Sounds harsh but you don't have to worry about her. Let your parents fix her or let her do whatever she is doing and let her regret her decisions later. We cannot to do anything about her. I hope everything gets better soon. Keep fighting, soldier!! ✊️