Who called the police?

Some “zero-tolerance” school bureacrat or teacher. E.g., an asshole with no common sense.

What cop/DA decided this was a good idea to charge a kid?

Same as above: an asshole with no common sense. Or a sociopath, neither would be surprising.

What parent presses these charges?

A pussy who expects the state to solve all their problems for them. In the old days the girl’s father would just go have a man to man talk with the boy’s father and let it be known that the boy is not to mess with the girl, or else…

What 14 yo girl is so upset by this that she has the police contacted in the first place?

Given the kind of parents involved (see above) probably a complete mental midget who’s been raised to appeal to authority to solve all her problems for her. IOW, a pussy.