I just realize you may not know what I mean by “tired” above. I don’t mean cramping or anything. Just that she might not have the energy to keep on singing quite so high. Her voice would still sound fine, and it wouldn’t hurt. You know, sorta like how, after a workout, even if you don’t stress yourself, you might not be able to work quite so hard for a while until you get some rest.
There’s a huge difference between that and actually hurting your voice, like Grande apparently did. Singing should not make you hoarse or hurt. (A little hoarseness is more common in the pop scene, as few sing with “perfect” technique, but not for days afterwards. That means you hurt something.)