Does First Time Sex Delay Periods?

my girlfriend and i had our first intercourse at the 2nd day of the month and she was supposed to have her menstruation at 4 or 5th day, the problem now is that she hasn't have it yet and its already 11th of the mo. we used condom and the thing is, i didn't come inside her, no signs of pregnancy on her shes just delayed, is it really true that first time of sex especially when it is hurt full could delay her menstruation?