Your sister's daughter is your niece. Note the apostrophe s on sister's, because the girl 'belongs to' your sister.
son is filius daughter is filia
she was the daughter of walter and hilary (bethanys parents), was the older sister of bethany, died in a car accident when she was 13, therefor bethany is her so to say clone.
The likely word is "niece" (daughter of your brother or sister).
The son of your brother or sister is your nephew. A daughter is a niece.
I discussed the procedure with her and her daughter. Though I prefer: I discussed the procedure with mother and daughter.
Nephew Sister's daughter is niece
brother, sister, or cousin
Your sister's son's daughter is your sister's granddaughter and your great niece. (Some would say "grand niece.") You are her great uncle or great aunt.
like the engliush word two
Your brother's sister is your daughter's aunt, and your daughter is your brother's, and his sister's, niece.
Your sister's daughter is your niece. Your sister's daughter's son (your sister's grandson) is your great nephew.
say their for your little brother/sister or son/daughter ... so on so forth.
Your sister's daughter is your niece.
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 sister's granddaughter are second cousins to each other.
bhagina
Your sister's daughter is your niece.
Your daughter-in-law's sister is not related to you, but is your son's sister-in-law.