Just want to ask that can I marry my aunt's daughter's daughter? That she's my niece but not of my father's blood. I love her. Can I marry her?

No, if this is YOUR... aunts grand-daughter, that makes her your 2nd cousin and yes in most places you may marry.

How old are you both now, and what does the girl say about your love for her?

Over 1/2 the Earths population is female. And people can't look beyond relatives for a mate?

GeoHive - Male / Female distribution (http://www.geohive.com/earth/pop_gender.aspx)

Actually, she's your first cousin once removed. Yes, does she love you and want to marry, and how old are you?