My girlfriend had a two week period. can she get pregnant after starting the pill today if we had unprotected sex?

Yes: You have to be on the pill at least 2 weeks to be safe. I recommend using a backup measure for the first pack of pills and after that to prevent spread of CSTD's. Use plan b asap to try to prevent pregnancy.

Of course!: I day of birth control is not enough time to allow it to work.. It can take 2-4 weeks depending on pill type and/or start date. To be safe, use protection for the time specified by the prescribing doctor.