At 15 mph it would take less than 2 seconds for a car at the back of a bus to reach the front of a bus. Are you suggesting that the driver of the bus was able to open and then close their door in less than two seconds? Alternatively, Are you suggesting that your daughter was driving slower than 15 mph yet was unable to stop?

I certainly believe there is room for discretion when officers write tickets, but not for passing a school bus.