Anger problem. A psychotherapist?

My sister has been known to be getting angry frequently from her childhood. When she was at home all of us knew about this and dealt accordingly by agreeing to all her terms. But she has been married for 7 years now and her anger has almost broken her family apart. She gets angry very suddenly and unpredictably to the point of hurting herself or even others physically. Later on when she cools down, she realises that it was her mistake and promises to never repeat that again. But she does the same again all of a sudden for very small unknown reasons. She doesn't even tell why she got so angry and sometimes she tells me that in that movement her mind goes out of control. I want to know whether this is a problem that can be dealt psychologically? She has many insecurities and reasons for depression in her life. But so do many other people. That's why I doubt whether to consult a psychotherapist?