You've gotten some good advice from most everyone. And this is tough. It's never a good idea to look at someone's e-mail, but I understand why you did it. But honestly, if you have a hunch that someone is jerking you around, you're probably right. Be that as it may...
First talk to your parents, since they know all of the stakeholders in this. Let them know what's going on and get their perspective. It's surprising how good parents often are with this stuff.
Then, I'd turn the tables. I'd tell her that you had "concerns". That things are getting back to you that simply don't add up and you feel like maybe she's sharing things with people that you thought were between the two of you, and when she's doing it, she's not really telling the whole story. Tell her it's really causing you concerns - keeping you up at night, giving you cause to question your friendship, wondering if maybe you've simply grown in different directions, etc. Then see what she says. I'm betting on more lies, but let her dig her own grave. Don't stop her, don't tell her that you know the "truth". And when she's done, tell her you appreciate her comments and are going to think on it a bit. Give it a few days and see what comes back to you from friends. Chances are that she'll spin it again and not learn her lesson.
At that point, you can go to her again and say, "Gee, roomie, our mutual friend just told me that you said blah-blah-blah and that was so far from the truth. I just don't know if we can remain friends if you're going to treat me this way" or whatever. Let her feel the consequences of her actions.
It sounds like you've got good instincts. If the relationship is important to you and you want it to work out, give her the chance to see the error in her ways and stop her behaviors. If she doesn't, at least you tried, and you can walk away with your head up.
Good luck, hon! Big hugs!