At most, it would be a verbal misdemeanor threat--similar to a ticketable offense.   The fact that the SRO officer is say "nothing is there" is helpful.  If they idiot dad does swear out a complaint, then your wife needs to counterclaim for a harassment complaint on behalf of your daughter.  These are both misdemeanors that really need to be handled informally, and the counterclaim/offense will punctuate that need.  If it was just verbal, most prosecutors will dismiss the case.