How do I deal with my mother's increasing combative behavior?

First, has she had a checkup lately? Medications can cause this behavior - or there could be one she needs and isn't getting. Interactions can cause this behavior. Some stages of Alzheimer's will be like this and there's not much you can do to calm the person, but I'd make sure a doctor checks the meds. Also, you may want to call the Alzheimer's Association for some personal help.
Good luck,
Carol