Who is Katherine Chinaski from Ham on Rye and what is their importance?

Katherine is Henry's subservient mother. She is described as quiet, and although she herself, seems to avoid abuse at her husband's hands..... we cannot say the same for their son. When Henry confronts his mother for her lack of interference, she tells him that the father is alright. She is either ignorant to the situation, or unwilling to put herself in the line of fire to protect her son.