Hello Mitch: Thank you for bringing your concern here to PC. I see this is your first post. So... welcome to Psych Central.

You asked if your S.O. is biologically incapable of not engaging in narcissistic type behaviors. I doubt anyone here on PC is going to be able to tell you that. I certainly can't. (I personally doubt anyone really knows for certain to what extent narcissistic behaviors are biological versus learned.) However, at least to my mind, I doubt it makes a lot of difference anyway. The behaviors your S.O. is displaying may have become so ingrained in her, as a result of having grown up with them, that whether or not there is a biological component may well be just a technicality. The important thing here, at least to my way of thinking, is that in order for there to be significant improvement in your S.O.'s behavior she is going to have to come to the realization she is doing what her mother did, make the commitment to change, & then seek the professional mental health treatment she needs in order to heal.

I know you wrote you've done a lot of research on narcissism. However here are links to 9 articles, from Psych Central's archives, that (hopefully) may help to provide some additional perspective with regard to your situation:

Narcissistic Personality Disorder vs. Normal Narcissism

The Female Malignant Narcissist is Just as Dangerous as Her Male Counterpart

What Are the Signs that You're in a Relationship with a Narcissist?

What to Expect When you Marry a Narcissist

11 Ways to Set Boundaries with Narcissists | Narcissism Decoded

https://blogs.psychcentral.com/narci...dium=popular17

https://blogs.psychcentral.com/liber...-false-claims/

https://psychcentral.com/blog/how-to...essional-help/

https://pro.psychcentral.com/engagin...es-counseling/

I hope you find PC to be of benefit.