You would be her aunt. She would be your niece.
Niece would be the most common term.
Your brother or sister's daughter is called 'your niece.'
If your brother-in-law's daughter is by your sister, she is your niece. If your brother-in-law's daughter is by someone else, she is genealogically not in your family tree.
If it is your brother's child, she would be your "niece." If the daughter is not fathered by your brother, then she is your "sister in law's daughter"
great uncle inlaw
If the brother-in-law's daughter is also your sister's daughter, she would be a niece. Otherwise, there is no relationship.
A neice.
If your brother adopted you, you are his son or daughter and his in-laws are your grandparents by adoption.
Neice
its called a niece
niece
Your mother's brother is your uncle. Your uncle's daughter is your first cousin. Any child of your first cousin is your first cousin, once removed.
shes called ur cousins daughter