Is it not compolsury to go to school in the US? In Germany families can get fined if their kids just don't go to or leave school (like in this case). Police even control spots like the city center or Airport in my city until 1 p.m., in order to catch minors skipping school.

And since you say "just let her go" I guess in the US the school is not fully responsible for the pupils? Like if a teacher let's a dimwit just go and said dimwit hurts himself or gets hit by a car during a time he should be in school, then the school will get in deep trouble.

Can't the teacher just close the door and call the police to sort this out with the kids partens? You guys even have police present at schools, seems like the safest and most logical option.