My Daughters hates us all

My daughter is 25, she is really going through a horrible phase. She hates her brother (20 years). He is only home weekends as he is in the army and she spoils our quality time together. She hates his girlfriend and tells her so. 
We have tried all strategies but she still spoils every weekend. She thinks we all hate her and exclude her but she makes it clear she doesn’t want to spend time with us when he is home.

This weekend it was his birthday. As usual we all go out for dinner but she said she wasn’t coming as “she” was going. With this she then flew into rage as we all still went. She told us she hopes we fall into a hole and die and she will manifest us all getting food poisoning. When we came home she was speaking to somebody on the phone and telling them we was going to try and get her sectioned  admittedly I said I am going to try and speak to somebody and get them to see her as I don’t know what to do  

I feel really hurt and feel her behaviour is out of control. She is ruining a close family. She is hateful towards us and yet so nice to everybody else!!