Anger arises from woundedness, and chronic anger from deep woundedness. It also arises from having one’s sense of morality offended (righteous anger).
The anger arising from woundedness needs to be addressed professionally by someone who is unprejudiced, compassionate and also honest. One who can look at it objectively and with an accurate understanding of where it’s coming from and why, and what is needed to heal it so the client can move on with a greater measure of peace.
Not every therapist is good for this.
Anger arising from an offense of one’s sense of morality is usually brought on by grave injustices seen in society and committed by society, or a segment of society. That kind of anger can drive good people to correct injustices, which makes us all a better society.
Wrath is one of the seven deadly sins, but that refers to destructive wrath, which is selfish and prideful.
I would suggest your friend seek professional help with her apparently deep-seated anger (volcanic eruptions begin from deep within the earth). She might also benefit from discussing it with her priest or spiritual director. The two sources for help needn’t be incompatible, provided the right people are involved. That’s what you both need to pray for – the right people who can truly help her.
I wish both of you the best. Anger of any kind can be difficult to deal with.