I did think about the "breadcrumbs" thing
But she's far too proud to ever want to come back so I'm pretty safe
I've never been able to do NC. For me, Low, impersonal contact has always worked best. Not sure what that says!
And yes, I totally agree re: she shouldn't be saying that to me (no matter how innocent it might be!). I still would never trust her. But strangely, somehow just hearing that she was sorry really helped me. It's all gone silent again now so fingers crossed that is it. Also, partly because I worry about her dying - she really IS a very poorly girl with a long term health issue - I don't know how I'd be able to live with myself thinking she died and we hated each other. I feel like some of the guilt has gone now, you know?

x
Maybe in that moment, it was completely real. Maybe she decided to give you the closure she couldn't give you 3 years ago. Maybe its a recycle attempt. There's really no way of knowing. It could be that if she has a terminal illness she's trying to make amends with those she hurt (and truly did care about). There are a lot of possibilities. I say that because of my experience.
I, like you, was NC with my pwBPD for 3 years. We were forced to ride together to a conference (company car) and she, like yours, apologized profusely about what had happened. I to this day still believe it was genuine. Time passed after that day and we had more contact. It progressed further (not rapidly, but it did progress) until we decided to give it another go. There was a long, serious discussion beforehand.
So how did it turn out? I was (basically) discarded again. It is a long story and still unfolding, but the end result is that her BPD caught back up to her (she started DBT, which made it worse). It's been one hell of a rollercoaster ever since I got back with her (though I was to infatuated at the time to realize it). It wasn't until we were both able to be around each other all the time that it quickly fell apart. I think she was more interested in the 'idea' of us than the 'actual' us (I guess that would be the honeymoon phase). She's still attempting to string me along (even though I just do pleasantries, as I am working my way to NC again).
If I had to do it all over again, knowing what I do now, I would've taken a page out of Curly (City Slickers)'s book:
Mitch: You ever been in love?
Curly: Once. I was driving a herd across the panhandle. Texas. Passed near this little dirt farm right about sundown. Out in the field was this young woman, working down in the dirt. Just about then she stood up to stretch her back. She was wearing a little cotton dress, and the settin' sun was right behind her, showing the shape that God had give her.
Mitch: What happened?
Curly: I just turned around and rode away.
Mitch: Why?
Curly: I figured it wasn't gonna get any better than that.
Mitch: But you could have been, you know... .with her.
Curly: Been with lots of women.
Mitch: Yeah, but you know, she could have been the love of your life.
Curly: She is.