Hi Pink_Flamingo,
Welcome to the BPD Family
I, like you found it a relief to put a name to the behaviors that I saw in my Significant Other's (SO's) undiagnosed BPD ex-wife (uBPDxw). Learning about BPD can really help the chaos make more sense. Keep learning what you can about BPD. I hit my local library and read everything I could.
I dared set boundaries (she was attacking my other sister for almost a year now) and I finally gathered the courage to tell her she was wrong and all hell broke loose. The abusive texts and emails are flooding in. 68 in 2 hours the other morning.
It sounds as if your sister had an "extinction burst" click on the link below for more information... .
Extinction BurstThe phenomenon of behavior temporarily getting worse, not better when the reinforcement stops.
https://bpdfamily.com/message_board/index.php?topic=85479.0In terms of getting your sister help, only she can decide to get help, you can't make her go, you can suggest it (like you did)but she has to want to go, want to make a change. I'm no therapist but an intervention doesn't sound like a good idea for someone with BPD. Your sister will most likely feel attacked and criticized.
What we can help you with here is understanding BPD, support for you as you learn more effective ways to negotiate the issues with your sister, we have tools that can help and we will listen and understand because we all get it.
Other members will be along soon to add their welcome to mine.
Take Care,
Panda39