Hi Marvelly
Welcome back here. I still remember your last post in which you talked about your sister's suicidal gestures. It is really tough dealing with a suicidal family-member so I can understand why you're struggling with this.
Your sister has been officially diagnosed with BPD but unfortunately her treatment and therapy have not proven to be successful so far. Her current behavior is quite concerning indeed. It's hard to tell for sure what triggered this, but she is really putting herself in danger by behaving this way. People with BPD often have an unstable sense of self so perhaps that could be a factor here. Another thing that comes to mind is that the thought of being in rehab or the fact that things seemed to be going better, possibly overwhelmed or scared her.
People with BPD are often very sensitive and can perceive what non-disordered people would view as innocuous events, as major slights or distressing events. Her getting triggered seems to be a result of her distorted thinking.
I am very sorry that she is currently in this troubling mental state, the worst you have ever seen her even. It is very sad that this has happened. We have some resources here that might help you with dealing with her suicidal behavior:
TOOLS: Dealing with threats of Suicide and Suicide AttemptsTake care