Am I understanding this right, your daughter made a gun from 2D and 3D pieces of plastics right?
I think this is mainly an issue for the teacher because your in the US, and you get school shootings so she/ he might be overly sensitive to these things.
What I can tell you is that if this would have happened here, the teacher wouldn’t have even blinked (not in the US), knowing that kids are kids, they play, and experiment without any malice intentions.