if she takes it everyday. if she's not taking any medication or supplements (st john's wart, soy isoflavones, certain antibiotics, some antidepressants, a few others) that might interfer with the efficiency of the pill (knocking it down to 85-87%). depending on the type of bc she's taking the average is about 96-99% effective.
other facts: depending on the type, her body and other factors birth control can take 1-3 months work properly, back up birth control is always a good idea in the mean time.
ask her which form she use, how long she has been taking it, make sure she doesn't forget. if she has to take antibiotics use condoms for about two weeks after she stops taking the meds.
before you ditch condoms make sure you both get tested for STDs, STIs and all that ick.
ML
not to put the fear of babies in your head but i should say it just to say it. even if you don't cum inside her there is the slim chance of pregnancy occurring from the trace amount of sperm found in pre-cum, not always present in pre-cum, but more common after recent ejaculation.