Well the daughter will be your grandaughter and you will be a grandmother/grandfathther.
You're her great uncle or aunt.
Your daughter is you great nephews great cousin if u live in Australia ,USA ,UK
Your daughter and your nephew are first cousins. His daughter is your daughter's first cousin, once removed.
Great nephew
Nephews are the sons of your brother or sister. Therefore nephews who are not brothers to each other are first cousins to each other.
He is their Uncle and they are nieces and nephews.
Second cousins.
Second cousins once removed.
Your brother-in-law's children are your nephews and nieces.
Your brother's children would be your nieces and nephews.
It does not appear that Thomas Jefferson had any nieces or nephews. He had a daughter, a son in law and two grandsons. He also had an aunt and a first cousin.
A cousin, in all those difficult cases they are your cousins
If it's your sister then your sister, if it's your brother's wife then you sister-in-law