Audrey,
I am sorry you are experiencing this with your mom. Something that helps me sometimes deal with the way people treat me is to remember- the way someone treats you is a reflection of THEM, and not of YOU.

Your mom treats you this way largely because she can, and there is a deficiency in HER life that makes her this way. While she is your mother, I am not so sure I would encourage you to have a relationship with you. It seems to keep you in turmoil. It isn't something you are doing right/wrong that makes her react the way she does, and you cannot 'fix' or change the way she interacts with you. You can, however, change your situation by staying clear of her, for much of the time. Just cause someone is 'family', they aren't entitled to treat you poorly.

And, I would not encourage you to educate your mom on any of her apparent deficiencies- what a way to fuel the fire!