Your brother's daughter would be your niece. So she would call you Aunt/Uncle
brother's daughter relation
Your brother-in-law's daughter is your niece.
The daughter of your husband's brother is your niece.
The daughter of your husband's brother is his (and your) niece. Her daughter is his (and your) great niece.
The brother of a daughter in law is the son in law.
She is your Great Neice.
You brother's daughter is your niece, just as your sister's daughter is your niece. The English language does not have different terms for daughter of brother and sister.
I will call her niece.
Niece .
niece
Your brother or sister's daughter is your niece.
they are your cousin