Mean, Disobedient Four-Year-Old

Question: 

My daughter is 4.5 and I’m at my wits end. She is such a beautiful child when she wants to be. I just don’t know what to do anymore. She’s mean to other children. She has no fear of any authority. She is very mouthy to other kids, her preschool teacher, and grandma. It just seems that it depends on what mood she is in for the day as to which child I’m going to get. I’ve been at the library were the lady there told her to stop doing something and she completely ignored her. She’s told grandma she’s going to kick her ***. Most of the time kids will listen to others better then their parents, but not her. She doesn’t listen to anyone if she doesn’t feel like it at that moment. Please help. I’ve run out of ideas. Time Out doesn’t work and she really doesn’t have a special something that if I took it away she’d care. I’m finding myself getting really angry at her and yelling. This is not what I want to do, plus I get so stressed from dealing with her that I give myself a headache. Thanks for any advice. Amy