If she's on BCC AND she's reliable, then you have nothing to worry about. If in doubt, tho, (or she forgets--happens) then do what I said. Don't take chances until you can afford it. For example, right now my husband & I are using a method that is <100% reliable. But we are both philosophical about our having another child. We've only got the one, and our life is VERY stable, so it wouldn't be an unwelcome event.
Personally, tho, I wouldn't stop using a condom until I was married (or some equivalent).
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh