Did you see my first answer? My mom just starts screaming at me to do better when I stop doing well at something. Particularly instruments.
I wasn't telling you to fail, but instead to do so well in certain areas that your mom might be fine with your suggestion of droping a few.
As for going behind her back, uhm, communication is key, like in any relationship. If you have a cell, use it. A lot. Text or call at least once a day if you don't see her that day. Make the times you do see her count. Also, group activites are your friend.