On Facebook and Twitter I discuss bars, clubs, fattening foods, girls, and random details of my life which may not necessarily be rated G. My mother would have a heart attack if she saw any of my Facebook statuses. Speaking of Facebook, I actually made a second account for her to be friends with, and she eventually found my primary one and added me. At the time, Facebook didnt let you select audiences so I just ignored her request and never added her to my primary account.
You might could do that with Twitter? I mean, have a new account where you post whatever and continue to post in your old account with mostly G stuff. She might not know to look for a new account if your old one had similar activity. Hm...I feel like Twitter would find a way to ruin that though with your friends talking about your account to your old one or something, etc.
Can't she already see your previous tweets?