Thanks for taking the time to reach out for some help with your parenting question. Helping your daughter learn how to cope with her anger really offers you a great teaching opportunity and a chance to help her develop the skills needed to cope with her anger and it express it in healthy ways.
When your daughter is calm, sit down to talk to her about the issue. First, help her understand what you mean by "angry"- as this can be a bit of a vague concept to a three year old. Help her recognize the signs of anger- such as a sweaty palms, increased heart rate/blood pressure, etc. Help her develop a "staying calm" plan for when these signs start to appear. Healthy ways to express anger include things like jumping jacks to burn off energy, drawing pictures, slowly counting to 10 to calm down, and other skills that you could help you daughter develop that would work for her.