Mother reading emails, how can I prove this?

My mother is an evangelical politic who insists she is a Christian but of course lives her life judging me and my husband and our friends. We recently got into an argument and she brought up something I had said about her to a friend in a "letter." I said "Mom, I haven't written a letter to anyone in years, what are you talking about." She tried to avoid the question, and I kept grilling her about it. She then told me that it was a public blog I had written on My space years ago and she and my dad had printed it out. Of course that was a lie, I did not ever blog about my mother on myspace. So this was obviously an email she had read. Oh don't even get me started about how much she stalks my facebook, of course I have her blocked as much as I can. What I want to know is....if anyone else were in my situation how would you feel and what would you do. I'm 28, I live with my husband and my one year old. My parents have always done this to me and I've gone back and forth between doing something about it and just ignoring it.