Well you can't be that shiny new car forever! At some stage, that car becomes a beloved old vehicle which never lets us down. She's simply taken off her rose coloured glasses and sees you for who you are.
I'm concerned about the anxiety issues and her still raising the issue of her cheating. At some stage, she must let this go. Or let the relationship go. But for her to continue in this way is not healthy for either of you.
I honestly feel that it's time you have the discussion about moving past it. Thing is, each time she raises the issue and you reassure her, you're giving positive feedback for her behaviour. So she will keep doing it. It's time she learns how to either let go of the issue or to self soothe.
Is she seeing a therapist for her anxiety issues? If not, she should be. We all owe it to ourselves and our partners to be in the best emotional place we can be in a relationship.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.