My sister drives me nuts

I have two sisters, but only one drives me crazy. Why, you ask? She's the least helpful person in any situation. I cooked Easter dinner at my mom's this weekend (my mom has trouble with her shoulders, so she can't really lift or stir anything. Her job is to tell me what to do.). My sister, who still lives with my parents and pays no rent or any household bills whatsoever, set the table. That's it. Even then, as I'm running between rooms with hot food and knives, she's sitting there asking me to get stuff for her. I managed not to kill her; I'm proud of myself for that. How does somebody get that lazy? By the time I went home that night, I was wiped out. I'm sure she was exhausted from lifting her fork. Yes, that was unkind, but I'm only human.