How much should I pay my sister for staying at my house?

I will be out of town for several weeks. My 20-year-old sister is going to stay at my house during this time. (Currently she lives with our parents). The main reason she is staying at my house is take care of my two cats. She’ll also bring in the mail. In the unlikely event it snows, she might have to shovel.

My house is about 7 miles away from my parent’s house and farther away from her work. She gets free food and lodging with my parent’s.

My house is really nice and my sister looking forward to staying there. I’m wondering, how much should I pay her per week? I plan to stock up the place with groceries before leaving.