Unless you aren't concerned about pregnancy, always use protection. Always. There is no reason with a drugstore on nearly every streetcorner, walmart, grocery store, etc - for anyone to have unprotected sex.
We would have no way of knowing when your gf would/may/does ovulate. Statistically she wouldn't ovulate 1 week after her period started. However, you said it has been a week since her period stopped, which would make it approximately 2 weeks from the first day of her last period - this would be her most fertile time.
See, always wear a condom and you won't have these worries!
In 2 weeks, have her take a pregnancy test if she doesn't start her period. If it is negative, you can breathe easy.