The answer is probably more complicated than I can give, but two things come to mind. Dehydration and doing too much. The strenous workout may be more than she can handle at this time. Suggest that she reduce the intensity of her workouts a bit. Remind her that her body needs 48 hours after a strenuous workout to recover, and during that time she should avoid another strenuous workout. Light runs of LongSlowDistance, light swimming, lighrt cycling, shorter runs are suggestions for the second day. This 48-hour thing leads to the heavy/light schedule of running, where "heavy" and "light" refer to the stress on her body, not to her effort in doing the workouts.
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