You are her great-aunt/uncle. She is your great-niece.
Your niece's daughter is your great niece. You are her great uncle or her great aunt.
Your niece is the daughter of your brother or sister. That relationship is not ended by divorce. If your brother married a woman who already had a daughter (from an earlier marriage), then she would be your "step-niece", and this relationship would, technically, be ended by a later divorce.
Grand niece.
Your niece's daughter is your great niece. You are her great aunt or great uncle, depending on your sex.
Great-niece.
your 2nd niece...!
Your daughter and your niece's child are 1st cousins once removed.
My niece's daughter is my great niece.
You are her grand uncle (or great aunt) and she is your grand niece.
Your granddaughters and son have the relationship of nieces and uncle. Your granddaughters being his nieces and your son being their uncle.
No he did not. I am one of his grand nieces. He had one daughter.
They are 2nd cousins.
Your niece is the daughter of your sister. If you have more than one sister, you can have nieces who are also the nieces of your sister, since they are daughters of the other sister.