How to Avoid Becoming a Vicious Step Mother

The child that my friend gave birth to was the main character of a fantasy novel that I read in my previous life. Not long after his birth, this poor child grew up with an indifferent father and suffered from abuse at the hands of his stepmother. He left home only to proudly return when he became an adult and convict the wicked stepmother.
“He’s such a pretty child, and I feel sorry for him. If it weren’t for Amanda.”
[What?]
My foot steps while holding the child stopped.
[Amanda… Amanda…]
Amanda, that was the main character’s mother’s childhood friend, a native of a Korean-American family. That was my name.
“I’ll be the Duchess for Marilyn, at least for her sake.”
And, maybe, she can be a step mother who doesn’t pick on this child? How to not be the evil stepmother, Amanda, abuse this child even if she dies. Can Amanda be a good stepmother? Can the Duke, a cold northern man who blows a cold wind, and Amanda be good parents?