This is the number 1 reason many women get pregnant while on birth control pills. If they are not taken at the same time, every single day, there is a higher risk of pregnancy. Since she took the pills she missed, that doesn't mean she can't get pregnant on those days. Supposedly, if you miss your pills, it can take up to a month for your body to adjust and for the birth control to work again.
On a personal note, I got pregnant while on the pill. My daughter is now 15 months old.
Also, I just want to point out that make sure she knows that if she takes antibiotics, it will make the birth control pills ineffective for about a month.
The safest way to not get pregnant is using 2 forms of birth control at a time. I would consider using condoms and the pill. I would go get a pregnancy test just to be sure, as soon as she is late (IF she is late).

So she still took it every day?

While you are at a slightly increased risk for pregnancy, it's still unlikely.

Personally, I wouldn't fret over it too much.

You can miss one whole pill and still be completely protected. If you miss two pills, you are supposed to use back up birth control for a week of taking pills.

But since she actually did take them, she didn't really miss them. They were just late.

If it's not too late, you can use plan b. But make sure you use condoms until you've got the schedule back on track for a week.

But like I said, I wouldn't fret too much.