If they’re sisters living together and both in low-income brackets, I don’t understand why they…

We do coordinate to a certain extent (she cooks dinner one week, I do the next, take turns buying the milk, etc.) but one problem is that we have very, very different tastes in food. I’m picky to the point of it being a disorder, and I can’t expect her to live only on the narrow range of foods I like, so we’ve found it’s mostly best to do our own thing. Honestly I’m seldom jealous of the actual items she’s buying, so much as her freedom to just throw something in the cart because she wants it, or detour through the purse section just to see what they’ve got.