Just because other people were fine, doesn't mean everyone will be. There is no way to know for sure of any sperm leaked during this, and condoms aren't 100% effective anyway,
However, there is only a 5 day window in the month that a woman is fertile (mid cycle), so there are a lot of things to weigh up. This is why some people get away with unprotected sex and others do not. The best thing you can do is encourage the girl to get the morning after pill. This only works up to 72 hours after, if it has been longer, the coil can be fitted up to 5 days after to stop any fertilised egg implanting into the womb. After 5 days, you'll just have to wait and see what happens.