Hi C.,
I feel for you. I am just getting into this with my daughter, who is a bit younger than yours. She's starting to get major attitude when asked to do anything - she says her friends don't have to do chores and she doesn't see why she should have to either! You can imagine my shock at that. I explained to her that every person in our household has certain jobs to do. Daddy and I go to work and work hard, she and her sister have to go to school and work hard, but THEN we all come home and we have a new set of jobs to do before bedtime. I asked her if it sounded fair that one person would get to sit around doing nothing while everyone else did their part to keep our household running.
When I put it to her that way, she understood. So then I said, ok, here are your choices of chores that I need help with. If you don't want to help your sister wash her hair while she's in the bath, that's fine, but you need to pick up some other chore. Finally she chose cleaning the kitty litter box, watering the plants indoors and out, and sorting the laundry into lights and darks. And I took over the chore she was rebelling against, which was helping her little sister wash her hair. Even my youngest, who is not quite 3, has chores as well. She helps sort clean laundry into piles by person, and then helps fold the socks. Also she is learning to set the table, as well as pick up her toys and put them away. So my oldest can see that she is not the only one being asked to help.
But I think the real problem is that she continues to go to school with children whose parents do EVERYTHING for them, and buy everything for them. I don't think that's good for children. What a rude shock it will be when they move out of the house one day, only to discover that the laundry and dishes don't do themselves!
So, I guess my advice is, listen to her concerns, try to compromise if you can, but ultimately you have to be her parent, not her friend. One day she will appreciate these life skills you are teaching her about responsibility and team work and doing the right thing.