there is always a chance of pregnancy whenever you have sex (protected or unprotected)...
if you are seriously worried about it then get the morning after pill...
good luck

If she has been on the pill for a year then she hasn't ovulated in a year. As long as she's taking it correctly, chances are that she's not pregnant.

Many women use just the pill to avoid pregnancy, myself included. If you're that concerned, use a condom next time. But this time I wouldn't worry too much unless she's missed pills or something.

Out of 100 typical women on the pill having sex for a year at an average rate, maybe 4 or 5 will get pregnant.

If you take it perfectly, meaning on time every day and you never take any drugs that interact with it or throw it up or anything, maybe 1 or 2 women will get pregnant out of 100 after having sex for a whole year.

So for you, having sex one time, and being one of those 100 women (or their boyfriend, lol) , the chances are pretty low.

If getting pregnant would ruin your life right now, go ahead and use a condom. You can never be too cautious. Using the morning after pill and the birth control pill at the same time every time is not recommended, but once wouldn't hurt.