I think this is more of a semantics issue than anything else. To use myself as an example, I don't use the word "sociopath" often at all in reference to myself. I seldom use the word unless someone I'm speaking to about the subject is more likely to understand the word "sociopath" as opposed to "psychopath"(the term psychopath is still largely misunderstood by many, though that has slowly been changing).

From what little you've said here about your mother, I certainly agree that the term "malignant narcissist" is most definitely an accurate label for her. She reminds me of a couple of people I used to know. How often did your mother lie, generally speaking?

My best friend had a malignant narcissist for a mother, my friend escaped her mother's home relatively early on in her life and I admired that(I had already been friends with her for awhile when she made the decision to get away from her mother). It takes guts for most people to really stand their ground with a narcissist. My friend cut off all contact, she's far happier now and she has a very fulfilling life... Though of course her mother was highly abusive and my friend does go to therapy because of course she has issues as a result. But she's made much progress with her issues, and I like that quality in a person to really face their problems/issues head on.