My ancestor
She would be my grand-aunt (unless, of course, she were actually my grandmother).
A grand-aunt is not technically an "ancestor", although I do rather like the recently coined expression "ancestral aunt".
Your nephew's daughter is your great niece and you are her great Aunt (or Great Uncle).Correction:Your nephew's daughter is your grand niece. You are her grand aunt or grand uncle.
Your niece's son's daughter is your great grand niece. Your niece's son is your grand nephew or your great nephew, whichever term you prefer.
Your sister's grand daughter is your grand niece or great niece. You are her great aunt or great uncle.
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.
You are her great-great Aunt (or great grand Aunt, depending upon your preferred nomenclature). She is your great great niece.
The great great grand daughter would be my cousin sister.
Great Grand daughter.
If you are a woman, you are great great aunt to your niece's granddaughter. If you are a man, you are great great uncle to your niece's granddaughter. In either case, your niece's granddaughter is your great great niece.
Your daughter's daughter's son is your great grandson, and you are his great grandfather or great grandmother.
Great Uncle.
Your aunt is your daughter's great aunt. Your daughter is your aunt's great niece.
Yes, your niece's daughter is your grand niece. You are her great aunt or great uncle.