I’m sorry for your experience. The pain of living with an angry person is real. Words are potential weapons that create long lasting wounds. ADHD may not be the only issue your wife has.
I am not suggesting that this fits but some people find anger has a pay off. It may be to maintain control, or to support her self esteem. Or perhaps she is just super sensitive to stimuli. Or is using her energy as a way to energize herself to keep going. And, although I hesitate to say it, you may be using her anger to support your life script. (as a participant in several relationships I found this to be my case).
But you, and she need to know that living this way is harming you and the children and yourself and is not ok.
Boundary setting is difficult but needful. It sounds like this is an ongoing problem and a response to a letter is by no means a cure. For your sake and the children’s, get help.