I had sex with my girlfriend on 24 November. Her normal date of period was 28 November. But now its 3rd December and she doesn't get her period yet.is there any possibility to get pregnant?

It's not likely, but it is possible. She should wait another week and see if her period is just late. If no period, have her try a pregnancy test. If it is negative, she should wait and see what happens when her period is due for December.

Be sure that you both are using some sort of birth control to lessen the chance of pregnancy.