She's unlikely preggers and well done to you guys for having the good sense to get plan B in the works. Plan B will make her feel quite ill because it fks with one's hormones. That hormone disruption should even itself out shortly.
To ease your minds, do what "dontaskme" above said and go out and get a pregnancy test, actually get two and then do them both.
In the meantime, tell her to take Tylonol for any pain just in case (unlikely) that she is pregnant as it's safe for both mother and child. If you're going to get an abortion (if in the unlikely chance she is pregnant) then it doesn't really matter what she takes for pain.
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion