Maybe you just have an extra sensitive sniffer?
Honestly, I never get close enough to my birds mouth to smell their breath to know how one smells compared to another.
It might just mean she has a different bioload than the others, if she's not sick I wouldn't worry about it.
Not sure what to tell you, but I wouldn't use anything unless you know what the problem is definitively.
If the chick is eating, drinking, pooping, and active..... the smell could just be an anomaly.