So, why do I think so much about what she's doing
She has been a big part of your life for years, so it is only natural to think of her and what she's doing.
and feel so vulnerable if she were to contact me; of which I think is inevitable?
If you feel that you cannot block her number and texts and emails, maybe these suggestions will help:
For the cell phone: I downloaded a "silent" ring tone, also copied it to notifications, and in her contact record, changed the audible ringtone and audible text notification to silent, and changed her text to "no notification" so that it does not vibrate either. I will eventually see that she has called or texted, but this way, I am not wondering if every text or call is from her. It actually helps.
For email: I created a new folder and have all emails from and to her automatically moved to that folder. Again, eventually I will see her email, but it does not show up "... .in my face ... ." at the top of the inbox.
If she does contact you about "feelings" and talk about your relationship, do not respond at all. If you feel like you must respond, then wait 24 or 48 hours. You WILL have a different, less reactive feeling after sitting on it for a day or so.
I know I can't rescue or even help this one.
Realizing that you can not fix or rescue them is a huge step forward! You are doing good!
So now I find out she's intruding into my social circle. What's up with that? What to do? I feel violated, disrespected. So now I have to go NC with what was originally my social circle?
I really feel for you and have experienced something similar with my BPD ex-wife.
She was socially connected to the wives of our 'couple friends', even though I tried to maintain those couple friendships, only one couple wanted to try to maintain friendships with both of us, the rest went with her. That was fine by me. I realized that I needed to move on to new friends and found that there were other separated / divorced parents with kids who were in the same situation, so we created our own group at church, and it has worked out well, new friends for parents and kids.