Hi Mitt,
I'm sorry you're in such a tough spot. Having to deal with a child with undiagnosed BPD while in the military must have been rough. And now, your wife has been seriously ill. It does seem like your BPD daughter hasn't accepted you marrying someone else, though her own mom is still in the picture and it's been 15 years. Alas, pwBPD tend to hold onto grudges as if their life depends on it. That actually may be the case, because they've created a narrative--an entire identity--around being victimized by "toxic" family members and boyfriends.
I wish I could say that things might get better between you and your daughter, but right now it seems she's determined not to have a relationship with you. That may be her very misguided way of "punishing" you for "abandoning" her and marrying someone else. If you spend some time reading these boards, you'll see that it's common for pwBPD to withhold contact with grandkids, as a form of control and/or punishment. You'll also see that abandonment is a key trigger for pwBPD.
I guess the bright side is that you can keep tabs on your daughter and grandson through other members of the family. Maybe they would be able to sense if there were any thawing of her feelings towards you, and that would be an opening to a potential reconciliation. I guess if I were in your shoes, I wouldn't write letters, but I probably would continue to send her holiday and birthday cards, just standard ones with the normal greetings, so that she knows you still think about her and "include" her. But I wouldn't expect any reply until she's ready, and I wouldn't be surprised if she threw out the cards without even opening them. As for your grandchild, your daughter has asked you not to send him anything, not even cards, so my inclination would be to respect her wishes. Nevertheless, I might suggest that you think about writing letters to your grandson (and maybe seeding a college fund), but holding them aside until your grandson reaches adulthood.
I'd also mention that in my experience with pwBPD/NPD, an illness can be triggering for them. I suppose that's because attention is temporarily diverted away from them, and they might feel "abandoned" again, as well as worried that time/resources/concern/attention are being diverted away from them. It's also possible that, because they are highly emotionally reactive, they feed on any negative emotions associated with illness--the pain, the stress, the uncertainty--it's highly unsettling for everyone, but super-sized for them.
I'll wrap up by saying that BPD isn't your fault, no matter how much your daughter tries to convince you otherwise. I think many parents on these boards feel tremendous guilt, along with despair and grief. I think you can let go of the guilt part.


