If you are a girl, your are your great aunt's cousin's granddaughter. If you are a boy, your sister is.
Your great aunt also has first cousins from whom you are not descended. For those first cousins, the granddaughter is your first cousin, twice removed, or your first cousin, or your second cousin once removed, or your third cousin.
First cousins, twice removed. Aunts daughter is your cousin. Aunts daughters daughter is cousin once removed Aunts daughters daughters daughter is cousin twice removed.
They would be your second cousin. Your great aunt is the sister of one of your grandparents. Your parents and the granddaughter's parents are first cousins.
Your grandson and your sister's grandson are second cousins to each other.
She would not be. You uncle's children are your first cousins and his grandchildren are your first cousins, once removed. Your children and your uncle's granddaughter are second cousins to each other.
The grandchildren of any of your great uncles and great aunts are your second cousins.
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.
Your granddaughter and your grandniece are second cousins or third cousins to each other
Your third cousins are the great grandchildren of your great great aunts and great great uncles.
Your great nephew and your granddaughter are second cousins to each other.
Your sister is her great grandaunt.
great great (etc.) grandparents great grandparents grandparents + great uncles and great aunts parents + uncles and aunts [=parents' siblings] siblings + cousins [=uncles' and aunts' children] children + nephews and nieces [=siblings' children] grandchildren great gandchildren great great (etc.) grandhildren also cousins and second cousins [=(great-)grandparents' descendants]
great great (etc.) grandparents great grandparents grandparents + great uncles and great aunts parents + uncles and aunts [=parents' siblings] siblings + cousins [=uncles' and aunts' children] children + nephews and nieces [=siblings' children] grandchildren great gandchildren great great (etc.) grandhildren also cousins and second cousins [=(great-)grandparents' descendants]