Hello Eyeamme,
I feel your pain... .
We are currently in the same situation with my husband's daughter (coincidentally also 34yo, we have 3 grandkids that are being affected by it also). The last 4 years have been rather turbulent and she's been on-and-off with us months at a time approximately half of the time on and half off.
Ever since we have learned about BPD and started to practice the skills and tools, our interactions w/my step-daughter have improved, however, there is always some incident or a boundary of ours over which she dysregulates and goes NC.
So, why am I writing this? To encourage you in this time of sadness, because we on the receiving end of the messages sometimes tend to take their words at face value, and that may increase our pain in the time of NC.
Usually, they do reconnect, following their own timetable (according to whatever is going on in their lives). What we can do to help speed it up is to open the door for them (not to go chasing after them, but to invite them, reach out, make it easier for them to connect when they are ready)
Let me give you an example (because the similarities are telling):
My step-daughter blocked our numbers and wrote us an e-mail a few years ago titled 'good luck and good bye' seemingly purging us out of her life forever only to e-mail later how we let everyone down by moving out of the country w/out saying good bye to the kids who would never see us again. (We hadn't moved and both times we sent e-mails opening the door for her, inviting her to re-connect. It took another three months before she called and left a message that she had a medical emergency and 'almost died'. We called back - the numbers were still blocked

My husband sent an empathetic e-mail and she re-connected with us. It didn't work the first or second time, it did work the third time. Why? She was ready this time and used the medical issue as a pretext, probably because she was too ashamed otherwise (turns out her 'almost dying' wasn't quite as serious either).
Lbjnltx and
Kwamina give some excellent advice. What I want to add to it, is perhaps repeat a bit what they say in a way - it is hard, it is painful, it isn't easy to accept. You would like to make sure you can keep a balanced positive r/s with your dd. You can only do your part. Your daughter controls the other part, so depending on what she does, it may or may not be possible and that uncertainty is heartbreaking and hard to come to terms with.
Yet, it is worth working on the skills and tools (including boundaries which may seem to push our pwBPD away at times) - all of the tools help making your life more stable and healthy and they help set up the stage for your daughter to respond in a positive way if she so chooses.
We recently had 5 really good stable months with my step-daughter, then she idealized her dad only to abruptly cut us off out of nowhere, according to the classic push-pull dynamic. Our numbers have been blocked again, we have opened the door for her. (it is sad, grandson's b-day is coming up, she has sent presents back in the past, he will most likely miss out this time as well). We will reconnect when she is ready. It does get easier with time, Eyeamme.