hi JUSTME I had a very similar experience with my UBPD mom earlier this year. She turned up on my doorstep after a year of NC as if nothing had happened when she had heard via my ex husband who she kept in contact with (stalking anyone?)

that i had had another baby. Initially i was pleased to see her as it caught me off guard and i was also loaded up with baby loving hormones but true to form she soon slipped back to her old ways. Snipes at my partner, snipes about our work situation, negative remarks about my brothers children and everyone else. The list was endless. I started to feel suffocated and that the relationship was out of control again.I went NC for about 2 months basically by just ignoring her calls (she soon gets the message nowadays) Then decided because i was feeling stronger after therapy sessions id write her an email outlining boundaries. Well once again we started seeing each other but she couldnt resist making her digs. You could almost feel her voice straining trying to find nice things to say.
Anyway i have finally made the break and ended things for good because unfortunately she is not able to see its HER with the problem If she were in therapy then it would at least give some signs she can acknowledge theres a problem.
I understand how you feel about her suddenley getting in touch.
I worry i havent seen the last of my mother although i am more or less positive she has finally thrown in the towel.
I think if she gets in touch with you she is more likely to be on her best behaviour rather than say something nasty, as she will want to draw you back in.Although you can never fully predict how they will react. I will never forget one christmas my mom turned up after 5 months of NC stoney faced and said can you get my grandchildren i have some cards with money inside for them but i wont give them you as you will steal it!

i threw her off the doorstep! What i know now about that is she was projecting because she used to help herself to my grandparents money

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Its certainly possible your mom will turn up unannounced or contact you at any time.They dont give up easily, it depends if she has found a replacement for you. I get edgy at birthdays or christmas holidays as those are the times she usually makes an appearance.
I think you are doing amazingly well to deal with this as it is soo hard and i understand completely how you feel. It is so irritating how no matter if they are in your life or not they usually manage to get you thinking about them. They are very disruptive and hard to predict . I dont know what more to say other than I am with you on this and know how you feel and will certainly take some strength from your ability to stand firm in your decision to remain NC peaceful and drama free. Sending you hugs and healing