Almost 5 year old is mean all the time

My daughter is almost 5, she is relentlessly mean and hard to be around. She is very demanding refuses to use manners. Screams for things to.be done now.( of.course we dont do it) until she uses.manners. tells us we are mean over and over. Talks in a mimicky, mean voice. I have no.idea where she gets.it.from. she literally make me cry. Refuses to say sorry. If we dont give her what she wants she will say" then im gonna yell at you". I cant handle it. Does she need therapy?