I feel bad about yelling at my younger sister

I yelled at my younger sister today because she got on my nerves, but all day she's been so happy and sweet and that made me mad because I was in a bad mood today. Now she's angry and I feel bad...today is supposed to be her day to sleep with our dog who wakes up early, but when I gave her to her she asked me to take her and I said no, slamming the door in her face. She smacked my door saying she hates me. Now I feel bad but she won't give me the dog to sleep with. I feel terrible, I guess I'll take the dog tomorrow.