You handled it much better than I would have. You were able to see when your anger was rearing it's head and back off fom it. That's really a major thing. You should be proud of yourself.
I find it interesting that with her behavior she's the one that felt compelled to snoop. I don't think I would have told her "it's ok". It isn't. One think I've (finally) learned is that if someone apologizes to me I can just say "I understand" or "thank you". Somehow, it's ok seems to minimize the damage they've done.
Her "but I'm the one who has to live with it" just p!sses me off. It's selfish and she isn't looking and what the cost was to you. It's BS. You really have no idea what she got into and whether or not she's lying. I told you you did better than I would.
You're right that is is what it is. If you log on under a new name....we'll find you.