Her grand great Aunt.
Your niece's son is your great nephew. You are his great aunt or great uncle.
Presuming your son is also your wife's son, the your wife's aunt is your son's great aunt and he is is her great nephew.
Your aunt is great great aunt to your son's daughter (your granddaughter). Your granddaughter is your aunt's great great niece.
You are your nephew's uncle, or aunt, and his son's great uncle, or great aunt. Your nephew's son is your great nephew.
Her grand great Aunt.
You're a Great Aunt to your nephew's son, who is your great nephew.
Your niece's son's son is her grandson. He is your great great nephew and you are his great great aunt or great great uncle, depending on your gender.
That's easy cousins.
Your great grandmother's sister is your great great aunt and your son's great great great-aunt. He is her great great great nephew.
Your niece's son is your grand nephew, and you are his great aunt.
Your great aunt is the sister of your grandparent Her son's son is her grandson. Her grandson and you share a great grandparent and thus are Second Cousins to each other.
Your grandmother's sister is your great aunt. Her son's daughter's son is her great grandson. You and your great aunt's great grandson are second cousins, once removed.