Welcome...I'm sad and mad that you have to deal with this.
Your mom sure sounds unstable no matter what. You are right to take care of yourself and set your boundaries.
I have a friend who's (now ex) husband (big time N) had been lying to her for years and having anonymous sex with many men...basically living a double life. She is understandably angry and wounded. One of the things her own (grown) children have asked her NOT to do, is make comments about thier dad in front of them. They totally understand that what he did devestated her, and think he's a jerk, but he is still their dad, and do not want to be in a tug of war between them. They confided in me, that they love their mom beyond description, but feel repulsed by her apparent need to compete unecessarily for their love by saying cracks about the dad. My friend is really working hard at healing and is open to changing her insecure patterns with her daughters.
Your mom, however, may NEVER understand what her badmouthing of your father does to you....and more importantly, does to your opinion of her. This inability to give you what you request and her "black and white" reaction to it, more than anything describes her as a real narc.
It sounds like you are doing a good job setting your limits. Her matyr comments are meant to hook you into taking on her pain again. And that is something nobody can do for anyone.