Obviously the mother is a twot! Yeah if the girl had been kissed in private fair enough, but a peck on the cheek in front of the school? Nonsense. Still, in this day an age you basicaly can't go wrong by staying away from other peoples sprogs, safe bet.
Is this right and fair? Maybe not, but since when did fair ever come in to it. Bottom line, if it aint your kid, stay well away, then you are safe.