There's no reason she shouldn't workout every day. Professional athletes work out every day for hours and hours a day and it doesn't harm them.
It's possible to overtrain if you're not in good enough shape or if you're not getting enough nutrition to support your training, but a regular 30min to 1 hour workout? Nah. Nothing wrong with that.
If she starts to feel exhausted or is starting to struggle with her workouts, then she should probably take a day off. And if she's weight lifting, then she shouldn't work the same group of muscles two days in a row.
But getting headaches is generally not a sign of overtraining - although if she doesn't go to bed until late, it could be a sign of lack of sleep!
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