I don;t know either. I hope we will get to find out. I have three borderlines in my life (MIL, aunt by marriage and long time friend from childhood) and have come across about three more in my practice. Only one was into cutting that I am aware of. Three made suicide attempts or seriously threatened.
All have zero damn memory of the things they have done or things that occurred in the past. They completely remember them the wrong way. Only a couple have been sexually promiscuous as most are supposed to be.
I think while some of that is common, none of it has to be there for the person to be diagnosed. For me, the constants are intense fear of abandonment that results, inexplicably, in crazy behaviors that ensure they will be abandoned - rages, pulling the person in and then shutting them out, intensive boundary crossing (like the allegation that LT picked the locks and watched her sister come out of the shower, if that allegation is to be believed) but extreme distress or rage if anyone ever tries to pry into their business, and then it's the idealization which swings to hatred.
I could see some of that applying to LT. She idealizes her husband. Let's see if she turns on him. She seems to maybe idealize her babies but then hates them as they age? I don't see evidence of intellectual disability in her actions or facial expressions in the videos, narratives about her, etc. In fact, she seems pretty sharp. "No, we don;t call him James. WE call him Jonathan!" Her ability to keep things hidden. Her close control of her son when he went to college. her stated desire for a reality show. her communications on FB, like to the fertility nurse? etc.
A huge cause of it is actually abandonment by a caretaker. From what I've read and witnessed, the primary caretaker not allowing for proper separation-individuation early in life and then in adolescence is not a cause as much as abandonment is (either physical or more often, emotional). And of course straight up abuse, physical and especially emotional.
I don't know about bi-polar for her. I don't know enough. Don't they tend to have issues with substance or alcohol abuse a lot? Anxiety and depression? The latter sure fits with hoarding.
I hope we will be able to find something out. I doubt it though. Usually that stuff is sealed.