Ok if you want figures, i'll give you figures
here it goes...
If your gf is taking the pill on the same time everyday and haven't missed one her chances of being pregnant is 1 out of 100
if your gf the pill on different times or what we call (typical use) it's 5-8 out of 100 chance
but here are the things that you should take into consideration...Since she already had her period...It means she's not really that fertile that time...And since she almost had took the pill for a month maybe she didn't even ovulate...So the chances would be slimmer estimated by about 1 out of 200 when it comes to (perfect use) and approximately 5-8 out of 200 when it comes to (typical use) I hope I did helped...
Well if you are still nervous she can take the pregnancy test (in planned parenthood) they can detect pregnancy earlier than home pregnancy test does...
If you have more questions...I suggest that you can visit websites like Plannedparenthood.Com or Teenwire.Com they kinda have a faq portion...It is really informative...
Sorry for my long reply..