What is a fair amount to charge my mother for living with me? She is also paying other caregivers to come in while I'm at work.

I work 12 hour shifts so on those day I don't have much to do, no meals to prepare or even getting ready for bed, but on the days I don't work I take care of her totally unless I schedule a caregiver. I am claiming her on my income taxes. The caregivers also do some housework and give her showers, so I want to be fair. I also want to stay within medicaid / medicare guidelines, I heard I can not charge what an agency would charge. Any suggestions?