This is commonly either an adoptive mother or a stepmother (the biologically unrelated wife of a child's father).

Gardner's older sister became the second wife of his wife's father, cementing the ties between the two families.

She grew up under the eye of her single mother, who is constantly harassed by the wife of Lena's father.

Boshoff's mother, Anna, was the second wife of his father, whom together had 7 children in addition to the six from his fathers first marriage.

Yes, I'm what you call me, the childless wife of your father, but you're the child I never had.

The woman's daughter, being the new wife of the narrator's father, is now both his stepdaughter and his stepmother.

Never forget that, childless wife of my father.

He had been born of a secondary wife of his father and needed a stronger tie to the royal lineage.

His mother was Najjemba, the 2nd wife of his father.

Amanda could have this child as her own as sister, teacher, and the wife of Dixie Jane's father.