I'd use her name. If the Brother in law is married to your sister, she would be your nephew's wife. And you are not related by blood.
what i call my father elder brother's wife
Your wife's brother is your brother-in-law.
Your sister in law is your husband's sister or your brother's wife.
Your Brother in law's wife
Your wife's brother would be called "brother-in-law".
younger brother's wife -- maradalu elder brother's wife ---vadina
The brother of your wife's cousin is also her cousin. You can call either of them "my wife's cousin." You are not related to them.
what i call my father elder brother's wife
Your wife's brother would be called "brother-in-law".
what i call my father elder brother's wife
Brother-in-law
Your brother's wife is your sister-in-law.