Re: The immovable object.
What specifically did she apologize for?
One interpretation from a far distance is that she sees you being supportive husband in very troubling time. She KNOWS that she hasn't treated you the best over the course of your relationship. The scales are tipped so far in one direction, that even she can see the inequity of it all.
She sees apology as clear-the-air attempt at a giant rug sweep. "You know all those years I ignored your needs. Yeah, those. Well, my bad."
Your milquetoast response to her apology is not sufficient to fully assuage her guilt over past treatment. If you make a big deal about apology, it translates into being something sincere and meaningful - a watershed. I suspect you would see it as something less - something more akin to rug-sweeping years of mistreatment.
No good answer here. But if she continues to push on apology front, I would counter by saying that you're less worried over apologies over the past and more focused on your relationship for the future. You wife can and will beat this, and when she does you want the foundation in place for a good relationship moving forward. For the apology to have meaning to you, it has to be tied to commitment to action moving forward. For you, that means that you expect X, Y and Z from your loving wife. You pick the X, Y and Z that are meaningful to you.
Or you can continue to marinate in your resentment and excel in beating everybody else at the martyrdom game. You can't change the past. But if you don't take actions to shape the future, the only one you can blame is yourself.