How much breast milk to leave with my mother?

I am one month pp and breast feeding. I have some milk in the freezer. My husband and I are going out on a date for the first time since I had our baby. My mother is going to watch her for 2-4 hours. She eats from the boob about once every 1.5-3 hours. I want to make sure I leave my mom enough frozen milk. How much would you bring? I think she eats about 2-3 ounces a feed but I am not really positive since I can't see how much shes drinking when breastfeeding? Any thoughts. I have a little anxiety knowing I am leaving her for 3 hours so I am probably way over thinking this....