Your third cousin.
Your granddaughter and your first cousin are first cousins, twice removed, to each other.
Your son and your sisters child are first cousins. The granddaughter is out of synch by a generation. That will make them first cousins once removed.
Your 1st cousin's granddaughter would be your daughter's niece.
Some of your granddaughter's first cousins are also your grandchildren, others are not related to you at all.
If you and someone else have grandmothers who were First Cousins, the parents of those grandmothers were siblings and you and someone else have great-great-grandparents in common. Therefore you and someone else are Third Cousins.
They are first cousins once removed. Your niece's children and your grandchildren will then be 2nd cousins.
Your son and your first cousin's granddaughter are second cousins, once removed, to each other.
First cousins twice removed.
The granddaughter is the niece's first cousin once removed.
Your husband's first cousin's child and your daughter are second cousins to each other.Your husband's first cousin's granddaughter and your daughter are second cousins, once removed, to each other.Your husband's first cousin's granddaughter and yourgrandchild are third cousins to each other.
Your child and your sister's daughter are first cousins. Your grand child and your sister's daughter are first cousins, once removed.
An uncle's nephew and the uncle's child are first cousins to each other. The uncle's great granddaughter and the nephew are first cousins twice removed to each other.