That's a pretty big overstatement of the impact you can have on a narcissist. They can pretty much get over anything even if initially distressed. It's temporary. They will have rationalized it in a way that suits them in no time. I gave up on my NPD father and it didn't take him long to conjure up his own distortion to write me off.

What you are looking for isn't actually remorse so much as change. You want her to change and be sorry. Historically, she's shown a pattern of not showing remorse and not changing. NPD aside, you can't change other people. You can only change yourself. That's what has to be accepted.