Moofqueen, I'm sorry that you're having these experiences and I hope that you'll find some relief.
There are many, many resources out there for disabled people. Far more resources for disabled than abused, and that is a fact. It may be a very good option to contact your local Social Services office and learn what your personal options are.
As far as an abusive parent goes, if you're living in her environment and she is abusive, then she will continue to be abusive. That's it. And, given the fact that you are disabled, she's going to use that to her advantage, as well. If you MUST remain in her environment, the only technique is to "grey rock" her. That is to view her as a piece of rock. Sounds may issue out of the hole in her face, but they are simply noises coming from a rock. But, the constant fact in this situation is that she will continue her abusive behaviors and NOTHING is worth remaining in that hurtful environment. Hitting her back isn't the answer, unless it's in self-defense. Trading a slap for a slap is answering violence with violence, and the cycle is going to continue until you take steps to break it. Remaining in that environment is NOT going to break the cycle or help you, one iota.
As I typed, there are countless resources available to the disabled, including counseling therapy. I would strongly urge you to consider learning what your options are, especially if you are NOT a minor child. I would urge you to investigate every option available, including assistance dogs and other means that will help you to become independent of ANYone. Abuse never ends. It only escalates. At some point, you're going to decide that you're a valuable human being and take steps to recover and become the priceless individual that you are. The only way to accomplish that is to get out of that environment. As long as you remain in the environment you're in, you won't want to do anything for yourself because the abusive mother will make you believe that SHE is the only person, on earth, that can see to your needs. And, that's simply not true.
My most sincere best wishes and brightest blessings to you
There are so many resources available for the disabled, seriously. From housing to assistance dogs, which is what I was getting at - not like a puppy, but an adult dog that helps with everyday tasks: finding keys, carrying mail, turning lights on/off, etc.