Spotting can be a sign of pregnant when it comes roughly 10-13 days after intercourse. "Implantation bleeding" usually comes just before an expected period, and is rarely noticed.
If she spotted in the middle of her cycle then had a period it's most likely the birth control causing the spotting. If it keeps up, she should ask her doctor about it, but it's fairly safe to assume she isn't pregnant.
Sometimes, when you remain on the same birth control for that long, spotting occurs because the body isnt getting "normal" periods while on b/c....it might be time for her to either switch pills or get off the pill for awhile...she needs to see her doctor.