Hopefully the heat and exertion was just enough to trigger her asthma. I personally haven't heard of exercise induced asthma as a s/s of MS although I would imagine someone who reacts negatively to the heat might respond with breathing difficulties if they have asthma.

My super charged running friends have also reported the 10 mile mark being where things start to go south when they run the half marathon. FWIW I haven't had MS issues related to being overheated and I run although never more than the 5k. Kudos to your daughter for being so fit.