My theory is that I firstly wouldn't want to arm-wrestle your daughter!
Just kidding, but it sounds like she has a, shall we say, firm grip, managing to bust a front canti. My reckoning is, the brakes being harsher than she is used to, the front wheel locked under emergency braking with the added leverage of the original brake lever - maybe with a small rut or similar to help it lock up.
The fall somehow managed to dislodge the return spring out of one arm, leaving no opposing force to balance the brake leaving one arm tight to the rim.
The "quick job" done to sort it was releasing the noodle, popping the return spring back in place and re-inserting the noodle into the stirrup