Let's approach this systematically.
Your mother's and father's parents are your grandparents. Your mother's and father's siblings are your aunts and uncles and their children are your first cousins. The children of your first cousins are your first cousins ONCE REMOVED (thereby establishing both the relationship and generational standing)
The siblings of your Grandparents are your great aunts and great uncles. Their children are your parent's first cousins.
Therefore your great aunt's niece is your first cousin, once removed, or she may be your mother.
If your great aunt is related to you on your mother's side, then her nieces are your mother, your mother's sisters (you aunts), and your mother's female first cousins (your first cousins, once removed).
If your great aunt is related to you on your father's side, then her nieces are your father's sisters (your aunts) and female first cousins (your first cousins, once removed).
That's easy cousins.
Your aunt is your daughter's great aunt. Your daughter is your aunt's great niece.
You granddaughter is a great great niece of your aunt. Your aunt is your granddaughter's great great aunt.
If you are a woman, you are great great aunt to your niece's granddaughter. If you are a man, you are great great uncle to your niece's granddaughter. In either case, your niece's granddaughter is your great great niece.
Great great aunt/uncle. To your niece, you are the aunt/uncle, to her child you would be the great aunt/uncle. So you would then be the great great aunt/uncle of her child's child (her grandson)
Your sister's grand daughter is your grand niece or great niece. You are her great aunt or great uncle.
She is your father's aunt and your great aunt. You would be her grand niece.
Your neice's children are your grandneices and grandnephews. You are their great aunt or great uncle.
great great nephew and u wud be a great great aunt... i think :)
Your niece's son is your grand-nephew. You are the child's grand aunt, or grand uncle (whichever applies).
Your Aunt's niece is you (if you are female), your sister, or your First Cousin.
You are her great-great Aunt (or great grand Aunt, depending upon your preferred nomenclature). She is your great great niece.