Hi DhammaMamma;
So much of what you're saying makes sense -- that your biggest worry is how she'll manage after you're gone. You love her and would want her to be able to either take care of herself or have care set up.
And it makes sense that you're ready to try a different way of loving and caring for her, where you step back and let her have the opportunity to catch herself... or not, whatever she chooses.
Knowing really specific things that are dealbreakers for you is important, too, like knowing that it is not good for either of you to be in a car with each other.
What struck me about your list is that so many of those things are 100% under your control -- what great (true) boundaries. For example:
-you can choose not to get in a car with her
-you can decide if you accept contact from her (or not) over the next 6 months
-you control your visit frequency with her
-you're able to decline to participate in listening to abuse
-you can say No to transporting the dog
-and many more
That's a great list of true boundaries, which are under our control (versus ultimatums, which aren't). She can decide if/how she participates in DBT, and then you can decide how you want to engage with her, based on her choices. And you haven't given ultimatums or empty threats.
It's also nice that you have some positive things to look forward to, like potentially getting back to playing games online together, or catching up over dinner. Like you said, she's your daughter, and you love her. A "least bad" relationship between you two could look exactly like that -- enjoying low-stress, low-intensity interactions occasionally, so that your relationship stays neutral to positive. It may not look like a "Hallmark movie mother-daughter" relationship, and that's okay, because it's YOUR relationship.
Have you ever had to disengage from your pwBPD? How did it go?
I wish we could! The main pwBPD in my life is my husband's kids' mom (and her current husband has many NPD type traits). The kids are now 15 & 17, so we're on the home stretch, but the dysfunction from Mom & Stepdad bleeds over into our life and is pretty intrusive. I love the kids but it's been very difficult to be "required" to stay engaged with such strong PD behavior.
One way that I have disengaged from some drama is that in the past, if there was something the kids wanted to do with us but on Mom's time, we'd try to send "convincing" emails about why it'd be best for the kids, or proposing time trades, etc. Mom would use those as opportunities to: prove that she was the favored parent, badmouth my H, tell him that the kids preferred her, propose deals that were in her favor, etc.
Now, if there is something that the kids want to do with us but on Mom's time, my email looks like: "Hi Kids' Mom, does it work with your schedule for SD15 to do XYZ on Day at Time? If I don't hear back from you by Day/Time, I'll assume we're good to go and will do pickup at Time. Thanks; kells76"
Basically, I accept in advance that Mom may say No, argue, blame, etc, so I already don't get my hopes up for agreement. If she does, that's an added bonus, but I'm already positioning myself to decline to beg/rationalize/persuade. If she say No then I don't pursue.
If she doesn't write back, that's also an answer, so I don't get hung up on nagging her to respond.
If she says Yes, I say "Thanks, be there at Time" and I don't make small talk. She sees most interactions as a referendum on who is The Good One and who is The Bad One, so the less "target" I present to her (in terms of content), the better.
In a way, I think it's kind of like your idea to have your relationship with your D stick to known neutral-to-positive venues, like the online game and going out to dinner. We can choose the breadth of our interactions with a pwBPD, and sometimes, having a more limited, more structured relationship offers the best chance of it being neutral-to-positive. Because I limit my interactions with the kids' mom, there are fewer opportunities for her to start arguments or badmouth. This is ultimately better for the kids -- yes, they don't see us interact much, but on the occasional times they do, they hear us say Hello and discuss the weather in calm, polite tones. That's about as good as it's going to get.
...
If you ended up sending your D your letter, how did it go?