SHould everyone bring somethign to Thanksgiving dinner??

THis year i am having Thanksgiving dinner at our apartment. My mother is making somehting, my MIL is making stuff and so am I ..my sister in law doesn t live with her parents, she is 33 years old, single, and lives alone..shouldnt she also bring soemthing over ??? she said she wasnt bec her mother is bringing alot of stuff already..what the hell has that got to do wiht anything>>>>>?? any suggestiosn??