OP -- our moms are not really similar in personality, but I feel that I can identify with your situation because my mom has also completely disregarded me when I have told her that it was not okay for her to say certain things to my children. At more than one point, I have felt that we have reached "the end" and that I could never speak to her or see her again. The disrespect was just too hurtful.
But...my mom is 39 years older than me (she's 86 now), and, after some time would pass I'd start wondering if she was still in good health or even alive. I even subscribed to her church's newsletter so that I could be alerted if she was in the hospital or something (by the way, I'm still glad to be getting this, because one of my old friends from high school suddenly died last September, and my mom never even mentioned it to me -- but I know she knew about it since I saw her at his memorial service, and I was so glad that I saw the notice in the newsletter and got to go because I was able to renew a couple of old friendships, including my friendship with my friend's bereaved wife).
At any rate, what has been working for us for some time now is that we don't allow her any unsupervised visits with our girls. We currently visit her, as a family group, for about 1-2 hours every two or three months or so.
I've become so much more at peace now that I've just accepted that she's not going to ever respect me or any boundaries that I've set (even though she'll always feign agreement), or even remember that I'm sick of hearing, over and over again ad nauseum, about stuff like how my unpopularity in school made it really hard for my poor brother, who was two grades behind me, to make any friends because he was stigmatized as the brother of the weirdo...
Since I no longer waste my breath trying to explain, for the gazillionth time, why what she just said to one of my girls or me was not okay, I have soooo much more energy for relaxing and enjoying life!
Now, if she starts off on a tangent that I don't find acceptable for the girls or me to hear, I can do one of the following two things:
a) Change the subject. Example: "Hey mom, why don't you tell the girls about the time that you and your brothers walked home from school in that blizzard?"
b) If she's in a tenacious enough frame of mind to not be willing to change the subject, or if I'm so ticked off by what she just said that I just feel like I'm done with her and don't even care to try to change the subject, I say something like, "Oh, gosh, it looks like we need to get going." Since my girls aren't always quick to transition, I'll say something like, "Okay girls, you need to be finishing up (usually, at Mom's, it would be a TV show); we need to leave pretty quickly."
I actually haven't had many problems, of late, getting them to make this transition...and, forgetful as my mom my seem, now that I've formed this habit of not even confronting her about her misdeeds, but just "movin' right along," her inappropriate digressions have gotten less and less frequent.
The thing is, back when I'd get upset with her and explain myself over and over in some fruitless attempt to get her to listen to me and see my point of view, I was actually feeding into her control drama. I was giving her the power to make me angry! Once I realized that she really wasn't ever going to change, this freed me up to decide how, to what extent, and even if, I wanted to deal with her. And my decision to just get up and quicly extricate my family and myself from any negative interactions, has had a whole lot more impact on my Mom's behavior than all my years of attempting to appeal to her as a fellow human being.
Follow Mothering