thanks a lot for reply..cheers!
Unfortunately, menstruation is not an effective contraception measure.
Its a bit more complicated to get pregnant than most people realize. It all depends on ovulation. Even if she has abnormally short periods, or "spots" (the period comes and goes within an amount of time) the chances are very unlikely. Sperm can survive in the uterus/tubes what have you, for a few days. No matter how you look at it, if she was having a true period, it would take more than a few days for her body to be able to adjust and make the necessary connections.
And if your truly worried about it, go buy the morning after pill, keeping in mind it decreases in effectiveness the longer you wait. But i honestly wouldn't worry about it. Just get her a pregnancy test in three weeks to make sure?
I'm not a doctor, so don't take my word as absolutely correct, but if she was on her period then chances are she is not pregnant. Sometimes a period only lasts three days, depending on the girl. Mine are usually three days, sometimes four. If you are both concerned, she could take a home pregnancy test (keep in mind though that they are not ALWAYS accurate). The best thing is probably to see a doctor for her to take a pregnancy test.
Good luck.