So what has been accomplished? Nothing.You can't have 2 outs on the same player. If the local rules did call for an out for throwing the bat and the batter was actually put out on the play they are just simply out no further penalty
It just illustrates the flawed rationale of the local rule.
As has been pointed out, players (no matter how young) how do not know how to properly drop a bat place other players at risk. Calling Suzy out for throwing her bat does nothing to correct the problem.