She is your Great Neice.
Your brother's daughters are your nieces
Granddaughter
4 daughters, 3 sons.
Your grandson.
Are you asking what you call your brothers daughter? Well if you are your brothers daughter is called your niece.
You call your daughter's baby, your grand-duaghter.
You would call your sister's daughter your niece.
They'd be your cousin.
A niece
A niece
Niece
Your daughter's sister-in-law is either the sister of your daughter's husband or the wife of one of her brothers. If your daughter's sister-in-law is the wife of one of her brothers, then you would refer to her as your daughter-in-law since she is married to one of your sons. On the other hand the English language has no special term for the relationship between you and the sister of your daughter's husband. If you need something, you will have to call her your "daughter's sister-in-law" or your "son-in-law's sister." Perhaps your daughter has a half-brother who isn't your son, but whose wife is still your daughter's sister-in-law. In that case, this woman is not directly related to you. Not everyone likes to make such distinctions, and perhaps you could consider her to be an honorary daughter-in-law of yours, in the interests of friendship.