It is not unusual for old school mates and/or friends to connect (this is especially the case with online searchers like face book etc) If you trust her and she loves you, then there is no need to be concerned. If this turns out to be a daily routine, then you may revisit this question with her. After all, in a committed relationship the two partners ought to trust each other.
Try to see what comes out of it and do not make something out of nothing for now. She may feel intimidated and controlled otherwise which could make her try to vent about this to her male friend.