Probibility of my girlfriend being pregnant? maybe %'s please?

My girlfriend has been on tri-sprintec for a couple of months now. She takes her birth controll regularly everyday (granted not at the exact same time everymorning but always between 6-8am) We decided to have a quickie and didnt use a condom. I didn't ejaculate inside her and she (for some reason) procceeded to rinse herself out with water for about half an hour in my bathroom (idk if that makes any difference but i felt it was necessary to add) So, what might be the possibility of her getting pregnant? Based by women who take this pill and have sex, or others? Thank you for your input =)