Well, after looking online and examining my own cat, who is a boy, I'd say you have a girl on your hands.
The 2nd opening beneath her anus (her vagina) is much closer to her anus than it is in boy cats. And like you said, she's partially calico, and calico males are EXTREMELY rare.
Okay thanks guys i was pretty sure that she was a girl after spending sometime looking at pics of both but i just wanted someone else with cat experience to say the same thing =]