She chose… poorly.

The dangers of a medieval pone playing with modern weaponry.

The nade seems to be modelled after the M18 smoke nade, so it ain’t an explosive, but the smoke is toxic after prolonged inhalation, and it displaces oxygen, so it won’t be fun to be near. Not deadly very fast, but you certainly won’t wanna be there for long.
 
Although, only the artist can tell us what it’s based on, but the M18 seems to be the closest (very close) inspiration. It ain’t a flashbang cuz those were either of diff model or totally diff colors than that, so with 99.999% certainty it ain’t a flashbang either, and I don’t remember seeing any explosive nades of that modeling and coloring.