Your sisters daygter is your neice!
None. She is your daughter's sister -in-law.
Your daughter-in-law's sister is not related to you, but is your son's sister-in-law.
Being your sister's brother or sister you would be an uncle or an aunt to her daughter.
You are the great aunt/uncle of your sister's son's daughter, and your sister's son's daughter is your great niece.
Your sister's son and your daughter are first cousins to each other.
Through marriage your step - sister's daughter is your step-niece!
I guess you will be her uncle. Consider this case.. You have a brother and he has a daughter.. Your daughter will be a sister in law to your brother's daughter.
Her aunt
Since your uncle's sister is your aunt, her daughter would be your cousin, just as your uncle's daughter would be.
their aunt or uncle
Your daughter and your sister's child are first cousins. Your daughter and your sister's grandchild are first cousins, once removed.
If your brother-in-law is your spouse's brother, then his sister's daughter is your spouse's niece, and your niece, too. If your brother-in-law is your sister's husband, then his sister is not related to you, and neither is her daughter.