great niece
You are her great-aunt/uncle. She is your great-niece.
You are the great aunt/uncle
Your brother's daughter is your niece. You are her Aunt or Uncle.
Your niece's daughter is your great niece. You are her great aunt or great uncle, depending on your sex.
Your daughter is your brother's niece. Your brother is your daughter's uncle
To your sister's daughter you are an aunt (or uncle) and she is your niece. To your niece's daughter ( your sister's granddaughter) you are a great-aunt (or great-uncle) and she is your grand-niece.
Your sister's daughter is your niece, so you are her aunt or her uncle.
Your sister's daughter and your sister's brother are niece and uncle to each other. The daughter is the niece of the brother and the brother is uncle to the daughter.
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).
Your nephew's daughter is your great niece. You are her great aunt (if you are a woman) or her great uncle (if you are a man).
You are her grand uncle (or great aunt) and she is your grand niece.
She would be your niece. and you would be her uncle.