How much can I charge my parent living with me?

My mother moved in last month and is having medical problems. She is 86. I am her POA and power of health decisions. My wife and I are taking care of her. There is not that much left in her savings (40K or so) and no other assets, but she won't have any expenses living here with us - she also receives social security of approx $1,500 a month. I am filling out a 'family caregiver' form. Has anyone ever done this personally, and how much did you 'charge' your parent? Since I would receive her money after she passes, I do not feel guilty 'charging' her, but want to make sure it's not too much. I went online to check out prices for a live-in caregiver who would do exactly what we do for her, and the cost is outrageous! Do people actually pay upwards of $15 an hour for 24/7 care? My calculator result shocked me! Really, the only question I want answered is if $1,200.00 a month is too much if Medicaid was ever needed later on. Since we aren't using her savings, she would use that for the first few months of a nursing home care, anyway, but when that ran out, I don't want to be accused of 'gouging' my Mom. Anyone with REAL answers, and not speculation would be so helpful. Also, I will not be rec'g any cash from her. This caregiver form (which will be notarized) is only to be used if Medicaid questions why she used her credit card to pay for Costco or groceries, which is what she wants to pay for each month. It is her money and we are letting her pay for it. Thank you.