your 2nd niece...!
Grand niece.
You are her great-great Aunt (or great grand Aunt, depending upon your preferred nomenclature). She is your great great niece.
Second Cousin
Nephews and nieces
Your daughter and your niece are first cousins. Your daughter than your niece's son are first cousin's once removed. Your daughter's child and your niece's child are second cousins to each other.
Your daughter and your niece's child are 1st cousins once removed.
Your borther-in-law's children are your nieces and nephews. You are their uncle or aunt, as is your spouse.
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.
My niece's daughter is my great niece.
They would be great nieces or great nephews.
They are your great nephews and/or great nieces. Alternately, some people say grand-nephews, grand-nieces.