General

You know the answer. She was wrong to do those things. Write her off, and keep looking. Good luck.

Towards what Eagledancer said (I'm not gonna quote it, it was rather long), I think that this situation goes beyond just personal rules. However, I do think what you said was good advice, and I can see the problems that can be created by those kinds of misunderstandings, I think that you'd be hard pressed to find someone that thought going through other peoples' email is ok. This may not apply to email but going through someone elses regular mail without their consent is illegal and email should be appraoched in the same fashion.

I had an ex do the same thing. It was this site she saw messages from, actually. She went on my computer one day (I'm assuming out of insecurity, which it seems is a growing problem in women), and went through my history, I have my login for FF saved, and she read through all the little complimentary messages I had sent to girls on the site about their pictures or videos or what-have-you and accused me of "cheating". She claimed she could "no longer trust me" and for months I had to make sure that if I visited FF at all (which was nearly impossible as she watched me like a hawk) I had to delete my internet history every time. It was aggravating and made me miserable, and we eventually broke up, fighting horribly via verbal comments. I'd say that this girl you are speaking of was definitely in the wrong and her freaking out over something like that is definitely her own problem, since she invaded your privacy.