I could see the exhaustion happening continuously as she keeps doing it- being like needing to go to bed at the end of a performance from using so much energy at the beginning of her career, building strength and endurance as she got older. If she's been doing it her whole life, like her profile suggests, she honestly might start to feel some of the effects that Rex was saying... if you start working out too soon it hurts you in the long run, even without magic, that's a real life effect. I don't want to kill the fun cause she's an interesting character but I want to keep that in mind.