What's should i charge my grandmother to clean her house?

My grandmother is a huge hoarder and asked me to help clean her house. She is the type that you can spend hours cleaning, and come back the next day and its right back to the way it was. She said she wants to work out a business arrangement where I get paid a weekly amount to come help her for x amount of days. I know a cleaning lady would be expensive, but she is my grandmother so I don't want to ask her to pay a lot. But on the otherhand, because she is so messy its an extremely frustrating job. What do you think is a fair amount to ask her to pay me weekly?