I'm not sure that Nancy would've outright defended Adam, but I could see her possibly becoming like Sue Klebold, trying to explain his behavior and try to grasp why he did it, but still very obviously believing that her son was her precious little angel...
I could also seeing her just completely staying out of the public eye and isolating because of the trauma from losing her child she dedicated her life to taking care of. I believe part of Adam's motive for killing his mother was because he didn't want her to have to deal with the aftermath of his actions, or even sparing her from the society he viewed as rape. He might've outright resented her and Peter for having indoctrinated him into the culture he hated so much though, we'll never know. One theory I've heard for him shooting her four times was that it could have represented all four members of their family, which if so, I think would be out of distain.
I definetely don't think she would've ever said she wished Adam were never even born... Unlike Peter Lanza, I can see Nancy admitting that she might've been able to do something different in order to prevent Adam from doing what he did.