Is she pregnant ?

The other night me and my girlfriend were dry humping while I was wearing boxers and she had on cotton shorts and panties. I didn't want to ejaculate but I couldn't stop it from happening. It came through my boxers but I covered it with my hand. Some semen from one of my fingers got on her cotton shorts. What are the chances that the sperm on her cotton shorts could end up getting her pregnant? It was exactly a week after she had her period and I'm not sure how long her cycle is because I think it was a little later than usual.