Hi Jhrh,
So you're already familiar with
anosognosia and how hard it is to nudge anyone into therapy.
https://bpdfamily.com/content/how-to-get-borderline-into-therapyI found out in my 40s, that my mother was in therapy for PTSD when I was a child. I had only known about she going into therapy for depression when I was 17. Given all of that, I wonder how much more whacky my childhood would have been if she weren't in therapy. She didn't have a parent to support (enable?) her either like your dad.
We typically don't recommend suggesting a Dx of BPD with the person we suspect may suffer from it, as it usually goes about as well as you've experienced, sometimes worse.
As for your questions,
1. She likely means those things
at the time. PwBPD experience dissociation. She may be truthful in that she doesn't remember certain things. She could also feel shame, and be lying to deal with that shame. As Christine Ann Lawson stated in her book
Understanding The Borderline Mother, "lying feels like survival." PwBPD feel core shame, and this goes to your 3rd point. I self-cured pwBPD described it like this (paraphrasing), "a person with BPD feels 'my feelings don't matter; therefore, I don't matter and am unworthy of love."
This is why validation is key to reducing conflict, and this is tough when on he receiving end of verbal abuse and accusations.
https://bpdfamily.com/content/ending-conflict(See the Read More link at the end)
Your question 2? Anosognosia. Given BPD is a shame-based disorder, in addition to the emotional dysregulation, in short: no one likes to be told that they are crazy or defective. Would you? Would I?
My mother sent me to family therapy when I was 12, then abandoned me after one joint session. Decades later, my ex (mother of my children) did the same thing. I'm not BPD (I was cleared by professionals), yet it pissed me off.
Try the validation tools, we have more material here. There is a subtlety to it that can be missed.
Lastly, I'd say that your sister may be triggered by your stability and success in life because she doesn't have to emotional tools to find that herself. Thus, it's easier to blame.