I agree with the others who say that this is not an issue of "common sense".
My grandmother and I bump heads, and she might do what your mother did. I would have just told her that I took care of what I needed to on my end and will deal with whatever the consequences. She comes from a different mindset on multiple issues, and our relationship is multi-layered. She is my elder, and I respect her as such; she is also a woman, and I see her as an individual citizen of the world and life...her dynamic with her elders and others, the environment she grew up in, the men in her life, her children, her outlook and health.... When she tries to push her ideals onto me, I sometimes just tell her that we are coming from two different places and have two different methods for addressing the issue, that one is right for me and the other is right for her. If she won't let it go, then I will sometimes go further and explain why our views are different and then tell her not to try to force her issues onto me, that the way I handle it is healthy for me.... We have a good relationship.
We don't always agree, and we don't always rush to the agree-to-disagree stage of the argument. Because I know her and get where she's coming from, I don't read any ill feelings into what she's saying to me, and I don't get angry with her. I get that I am simply going against HER grain, the grain that was formed long before I got here. It's not personal, and it's not an attack. Also, she feels good enough around me to express her true opinions, and I don't take that for granted. (You see, she doesn't speak from her heart and soul when her audience would be someone who doesn't necessarily have regard for her heart and soul.) I use this method of receiving with both my grandmothers. I get who they are and where they come from, and I believe that they see me, as well. When they try to tell me what to do, I don't feel threatened by it. Instead, I appreciate that they feel comfortable enough with me to open their hearts and share how they really feel about something. The ones who only experience their closed mouths don't get to enjoy the richness of what they have to offer to a relationship. Those people get to enjoy hearing their words bounce off the walls when they think that they're speaking to these women. That's how I approach it.
How do I handle a relationship with someone with such differing notions that contact between us keeps our heads spinning--or at least mine? I limit the contact. When we are in contact, I avoid passionate topics. My husband's SIL is the only person who comes to mind regarding that extreme. I refuse to have a private conversation with her because she will run back and report her version of events, and I don't trust her to relay the conversation accurately. I honestly don't trust her to even experience it as it actually occurs. I can radomly say the word "green" and she will swear that I called her a "purple bear". I can't talk to people like that, because we do not speak the same language. She and I can hear the same words and interpret them completely differently, and it creates drama that I am simply not willing to engage in.