She would be your first cousin, twice removed.
"Twice removed" means that the relative has two of the same great-grandparents as you.
Your granddaughter and your grandniece are second cousins or third cousins to each other
Your uncle's granddaughter and your child are second cousins.
Your granddaughter and grand niece are second cousins to each other.
Your great nephew and your granddaughter are second cousins to each other.
You and the granddaughter of your great grandmother's first cousin are third cousins, once removed.
Your niece and your son or daughter are first cousins. That would make your niece and your grandchild first cousins once removed. Your niece's child and your grandchild are second cousins.
Your brothers granddaughter is your grandniece.
Your children and your husband's niece are first cousins. There is a difference of one generation between them. That makes them first cousins once removed.
It could be one of two answers. They could be third cousins. Or they could a first cousins four times removed.
Fourth Cousins, twice removed
Your granddaughter and your second cousin are second cousins, twice removed, to each other.
Your great great niece is the granddaughter of your niece or nephew. Your daughter and your niece or nephew are first cousins. Your daughter and your great great niece are first cousins, twice removed.