Helping a child overcome anger issues

There is a seven year old girl in our family who has anger issues. When she is angry or upset about something she tends to scream and throw things and forgets whether she is talking to an adult, or other older family members or friends or whether she is in a public place. Its impossible to reason with her then. Also, she gets angry without any reason at times and switches very quickly from happy to angry and vice versa.

Please tell what should we do and what should we recite so that she calms down and becomes less angry and stubborn over time.