Little sister..

So im 17+2 with baby #2 and my son is 14 months old and my husband and I just took in my little sister. She doesn't have a job, dropped out of high school, so we are basically doing everything for her. I am so upset right now! When she moved in we told her that she would have to help around the house. The only thing I ask her to do is was the dishes. I don't ask her to help with my son, clean the house, clean the entire kitchen or anything like that. And all she does other than the dishes is keep her room and bathroom clean. That's it! Well the past few days, I'll ask her to wash the dishes and she gets an attitude and rolls her eyes. Well today, I asked her, so said she would. I waited 2 HOURS! And she was still on the phone with her boyfriend. So I ask her if she's going to do them so I can cook. She rolls her eyes, huffs, and says yes. Well I waited again and nothing. So I go to do them. I guess she heard me turn the water on and runs out of her room "I was gonna do them. I hung up on CJ (her bf) so I could" I said "I got them. I've already started" so she just stands there. Am I wrong? What should I do? She acts like me asking her to just wash the dishes is the biggest inconvenience ever to her. I'm not asking her to clean the whole kitchen. Just wash the dishes. She's 21. She's not a child so I shouldn't have to stay on her like one. We buy everything. Her shampoo, her hygiene products, her food. We pay the bills. What do I do???