Scenario: A character, Sally, was with a party returning from a diplomatic trip when they spotted a large number of enemies heading towards one of their kingdom's outlying villages. As she has the fastest horse, Sally is sent to the main city to warn the king to send a force to deal with the attack.
The horse is in good condition, but isn't accustomed to flat out running for hours on end. When the enemy force was spotted, Sally and her companions had been on foot for several hours so the horse was fairly well rested.
What is a reasonably long time a horse in good condition with a female rider of average weight and height, wearing a mixture of leather, chainmail and fur and carrying a number of metal weapons including a sword, could run at full pelt for, if the rider is more concerned about her companions' survival than that of the horse?
What signs would tip Sally off to the fact that she's ridden her horse too fast?
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