wow i dont know what to say.
first of all im not gonna knock you because you know it was wrong, and you didnt post this to have us all go crazy on you, i can tell you are genuinely in a weird place about it and just wanted feedback.
i think if i were you i would just sever your "friendship" with this "friend" and try to walk away. hopefully that will fix it, and i sure hope her forwarding your emails with false info doesnt come back to hurt you, because you obviously cant talk to any of your RL friends about doing this.
it might be hard to walk away from her as you thought you were friends, but she doesnt deserve to be your friend if she is going behind your back like that. even tho it probably wasnt the right thing to do, you were just doing to her as she did to you. doesnt justify it, but hopefully you kwim
good luck!