Now we're talking. That girl should get expelled for this. Bullying, distruction of personal (potentially school?) property, and now assault (at least that could be a possible charge in the US) with the tacks. If it was only 1 tack, it could be taken as an accident, where one just dropped into the shoe, but 2 is implying intention, because of how improbable 2 tacks fell unnoticed, both landing spike up, into the same shoe.
Side note, how do you even miss that your shoe has tacks in them? They are not even closed. They are Addis flip-flops, sliding them on alone should either alert you to the tacks, or just clear them away.