Single mom struggles with disciplining her four year old

Hi Sara, I am a 25 year old mother of a 4 year old little girl. I am running out of ideas on how to discipline her properly and have her understand she has to listen or else there are consequences. I have tried time out in the corner and her room, taking things she enjoys away, quiet time etc. She is very bad because I let her get away with things for too long and now I feel its too late. I also have trouble with sticking to disciplinary actions that I am trying to enforce and I give in way too much! She says bad words at day care and hits and yells and also has been saying "I hate you" or "I dont love you!" to people when she doesn't get her way. I explained, as did her daycare, that these things she says are unacceptable and hurtful to people around us. People we do in fact love and care greatly for. I just dont know what else to do. I am panicking because she is going to start pre-school next year and I want her attitude fixed, but I want to do it right. Can you give me any ideas or pointers?