Your sister's daughter is your niece and you are her aunt (if you are a woman) or her uncle (if you are a man).
The daughter of either your sister or your brother is your niece. You are her aunt if you are a woman, or her uncle if you are a man.
Your sister's daughter and your daughter are first cousins to each other.Your sister's daughter's daughter (her granddaughter) is first cousin once removed to you daughter.Your granddaughter and your...
She is your niece, you are her aunt or uncle.
Niece.