I can't rule in or out the stories.
Unsubstantiated claims of victimhood, yes, there's a reason they're unsubstantiated.
But I can't sleep at night thinking there is a degree of truth to this seemingly unreal story.
Maybe. You may never know for sure. But you can't 'save' her, not even from herself. She is an adult and she has responsiblity for her own life. You can point her in the right direction but that's all. BPD is a disorder most evident in close relationships. As much as she claims otherwise, she can't really listen to you due to the emotional baggage of the past relationship. If she really wanted to get well, she would listen to you suggesting her to seek an experienced therapist, be honest with the therapist, apply the therapy and stick with it for years. No quick fixes, sorry.
I want closure and I feel knowing if she is sick or this is true will help.
Closure is something you generally won't get from a pwBPD, you'll have to
Gift Closure to Yourself. Let Go and Move On.