The daughter of your aunt is your first cousin.
The daughter of your great aunt is your first cousin, once removed.
Your aunt is your daughter's great aunt. Your daughter is your aunt's great niece.
Your great aunt's daughter's children (her grandchildren) are your second cousins.
She could be your grandmother. Or she could be your great 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.
You are the great aunt/uncle of your sister's son's daughter, and your sister's son's daughter is your great niece.
You are her great-great Aunt (or great grand Aunt, depending upon your preferred nomenclature). She is your great great niece.
Your brother's daughter is your niece. Her daughter would be your great-niece. You would be either her great uncle or great aunt.
Your sister is great aunt to your daughter's child. The child is your sisters great nephew (if a boy) or great niece (if a girl).
Your great aunt is your daughter's great great aunt. Your daughter is your great aunt's great great niece.
Your aunt's daughter is your first cousin.
Your great-great aunt is your daughter's great-great-great aunt.
Your great grandparent's daughter is either your grandmother or a sister of one of your grandarents. The sister of one of your grandparents is your great aunt. (Some people would say, "grand aunt", which means the same thing.)