I think there are so many things that could have happened to cancel out the pill.
I personally am surprised that more people do not fall pregnant on the pill.
I think there are several moms on this site, who became moms while taking the pill.
So, yes I do think it is possible. I suggest she does a pee on a stick test, and possibly some blood work if she is vaguely suspicious, she does not want to continue taking BCP if she is indeed pregnant.
Though if she had her period, logic should say it is unlikely ... but I have noticed sex, babies and logic, often do not seem to read the "logic" memo.