Thanks for the query.
Condom has a failure rate of 14%.
Since your girl friend is using pill , chances of failure is 0.2-2% depending on the type of oral contraceptive
In simple words her chances of getting pregnant are less than 2 in 100 users of OC pills.
So ask her not to panic and get a urine pregnancy
test done if she misses her periods.
Hope this helps,