Downloaded full resolution version, played with mplayer (command line), mplayer said it is 28FPS, I used "." command (frame by frame mode) and I counted 12 frames of flash starting 12 frames before the boom, so that's 478 feet all the way down to almost 0 feet +/- lots of error possibilities, but I am guessing a lot of the continuing flash was the light bouncing around and the bolt had already finished by then. Not only the bouncing photons, but it may have also caused something else to start lighting things up on its own too (such as a transformer exploding, causing more light later than the bolt, or a tree exploding, same thing possibly as it singes).
But ~0 to ~478 feet from what? As pointed out by others, probably some electronics was hit, possibly even further than 478 feet away. Often it's a transformer, and those things explode, as do a lot of other things hit by lightning (trees, etc.), so one is often lucky not to get a direct hit. Other posts talk about EM fields. I'm glad she is OK.