@olds She's nine years old, and while three hours may not seem like much, an average adult finishes a marathon in twice that time. Being unfit has nothing to do with it. The following comes from my experience doing competitive high school cross country racing: It takes weeks of training to get even a fifteen year old to run a respectable 5k time, it would be madness to ask a completely unprepared nine year old to even attempt such a race at a pace any faster than jogging. The aforementioned training is ~1 hour of jogging and one hour lifting weights Monday through Saturday, all under close supervision with plenty of water. If you asked us to run (as opposed to jog or sprint) for even an hour ( as opposed to her three), it would be the only thing we did that entire day. There would be intense training beforehand to prepare us for it- not just our coach telling us to go do it. If he did, he'd be fired and practically exiled. Running is not something to be taken lightly, and safety is paramount.
She did not die from a short sprint. She was told to run, not pace herself as even Olympic athletes must do, without water, for three hours in weather likely around 70 degrees Farenheit. If you expect an untrained nine year old to defeat a cross country team that regularly places in the top 3 in its regional championship, then I pity your future children. By your own words, you are "no skinny," so before you get on a soapbox and preach about a lack of endurance among kids, try to match her accomplishment. Remember, no preparation, no breaks, no water, race pace.
-Penguin