So sorry you’re having to deal with this. It sounds like you’ve been very considerate, so I can see why this would be hard to understand, easier from an outside perspective where emotions aren’t running high, e.g. a mediator or therapist.
This all makes no sense, and I have no idea ...... b) how to accept it while she continues to be hostile in our living environment.
“Reframing” the situation is one approach that may help. People with BPD fear abandonment and it sounds like your sister’s fight or flight reaction has been triggered off the scale. It’s worth reassuring your sister you're not abandoning her and understanding what support she’s worried about losing. A common theme in best practice approaches with someone with BPD is an empathic approach, which ironically is harder to do if it's a relative and you've been worn down over time. Also avoid judgment.
It’s a natural human technique to transfer blame when we can’t accept the consequences. Only in this case it defys logic and fact. That's likely the "cognitive dissonance" someone with BPD will feel when anxious. So addressing the rout cause, i.e. triggers, stress and anxiety should make your sister become more rational about this.
It’s likely the emotional consequences that your sister can’t deal with. Someone with BPD struggles with emotional regulation. There’s typically a neurological aspect to this, so it’s not just about learning to regulate; they have more intense emotions to deal with, and often need different coping mechanisms, which is where a trained therapist comes in. Avoidance is another way of dealing with that seemingly insurmountable tsunami of emotion. But a therapist can only run off the facts presented - it's likely your sister’s cognitive dissidence is making her a false reporter, so see it for what it is - fear.
This all makes no sense, and I have no idea a) how to get out of it ...
Change causes stress, which typically exacerbates BPD symptoms. Breaking the move down into smaller, manageable tasks should help. BPD normaly comes with issues with “executive functioning”, i.e. the very skills needed for a successful house move. Maybe she fears the loss of your support organising the household ? Behind this will likely be a fear of failure.
I'm guessing this isn't what you want to here, as it sounds like you are getting emotional exhausted by this and would ideally benefit from a quick fix. But eviction, i.e. sudden change so someone's fears can't fester, would be a lot harder for someone with BPD to deal with and risks "re-traumatization". That said, in my country if someone is seen as a lodger, rather than a tenant, it's easier to evict at speed.
Most importantly, get support for yourself first, you deserve it. Sounds like you've been extremely support already and should be proud of that (if your sister gets to a more stable condition she may well see that). Apologies for the long response, but I'm not on here often. If you get support from a therapist or conselor, they can step you through the process as new issues present themselves, or you could use this forum.
