I know she is ill but that isn't an excuse to treat me the way she does.

You don't say what disorder your mother is suffering from, but remember, her behavior may be the result of that affliction. Also, the elderly often take out their frustration on those they love most. I know its hard, but try not to take it personally. She may be acting out because she's frustrated and afraid by the physical or mental changes that are happening. Here is a link to a question/answer from another caregiver, who like you, is hurt and frustrated by her parent's behavior. I hope this helps!

https://www.agingcare.com/articles/dementia-and-undesirable-behavior-changes-how-do-i-handle-dads-profanity-112079.htm