step father in law
There is no relationship. She would simply be your first cousin's wife.
Husband and wife relationship is called a marriage.
your grandfather
father
A father and son relationship is called a paternal relationship.
The father's brother's wife is called "pedda naannagaru" in Telugu.
The English language recognizes no relationship between the parents of your father and the father of your spouse.
A father's mother to the father's children is called the Grandmother (aka: Nana; Gran, etc.) The father's mother to his wife is the wife's mother in law.
A father's mother to the father's children is called the Grandmother (aka: Nana; Gran, etc.) The father's mother to his wife is the wife's mother in law.
The second wife to your father if she is not your mother is called your step mother .
If your father's brother's niece is really your father's brother's wife's niece, then there is no genealogical relationship. Otherwise, she's either your sister or your first cousin.