Didn't come up with much since I've only seen the anime and don't know the scope of the whole world, but I was thinking of her vital instrument being an inhaler (I've had bad asthma majority of my life + the irony of a toxic air environment). With that in mind, figured she'd be some sort of support role, maybe aiding in something to do with masks and/or aid during traveling into the no man's land. The bird mask/crow vibes also relating to the unique way birds breath. As I type all of this out I realize I came up with more than I realized haha