I've Had Sexual Intercouse Last Night, We Did It Safe

I've had sexual intercouse last night, we did it safe until the condom broke inside of her. I didn't see anything as it was dark and 3 in the morning. I pulled out before i climaxed as i felt that the condom broke inside of her. I ejaculated all over the bed but my gf said that she felt a drop on her vagina. She was on the 4th day of her period. It has been 10 hours since this happened. How likely is she to get pregnant? Please help as we don't want any babies yet. We were in the Doggystyle position just to give you an idea of how it happened.