worried that she could be pregnant cause it was spotting.

Okay so a little over 3 weeks ago my girlfriend and I had sex and the condom broke. I immediately felt that it broke so of course i pulled out and we stopped from there. I didn't ejaculate in her but there might have been some slight pre-ejaculation present. So today my girlfriend had some spotting which she thought was the beginning of her period but it turned out to just be spotting instead. Now we are worried that she could be pregnant cause it was spotting. Her period is suppose to start in acouple days or so but it's hard to tell when actually cause she is very irregular. Sometimes having her period on the 5th week or skipping a complete month at times. So we are just worried about the spotting cause she has never spotted before. What are the chances that she could be pregnant?