My girlfriend is on the pill, she's in the second month, she takes yasmin but its a combined version, I mean she takes 21 pills and then she pauses for 7 days and starts again. This is what happened:

on sunday, day 13, we had unprotected sex (we usually use a condom), she took her pill as usual that same night, around 11 pm. ( she always takes it around this time). Monday we had protected sex around noon (we used a condom). But that night she forgot to take the pill, she remembered the next day and took it between 11:30 and 12:00pm we have not had sex since then. She took the rest of her pills on time (seven remained) now she is in the break and waiting.

What are the chances of her getting pregnant?,´we know that its normal to miss a period in the first months of the pill, how can we tell if this is happening? Opposed to pregnancy?. Any help would be appreciated.
Thanks