Nibling vs. Niece
Difference Between Nibling and Niece
Used especially as a gender-neutral term: the child of one's sibling or sibling-in-law; one's nephew or niece.
The daughter of one's brother or sister or of the brother or sister of one's spouse.
A daughter of one’s sibling, brother-in-law, or sister-in-law; either the daughter of one's brother ("fraternal niece"), or of one's sister ("sororal niece").My niece just celebrated her 15th birthday.
a daughter of your brother or sister