Getting over the embarrassment of being seen nude by my mother?

That sounds really awkward, and I wouldn't be comfortable with it either. Maybe instead of yelling at her about it sit her down and have a talk with her about it. Tell her that it is nothing personel and you know that she doesn't mean any harm, but when she does it she makes you feel really uncomfortable and that it upsets you, and that you have even considered moving away because of it. Make sure she knows to knock and maybe get a doorstop and wedge it in the door, take it out after your dressed but just use it as a precaution. Hope this helps :)