Well. Just read through what we've got so far. I think the most likely reason for her scent is that her family is spiritually important/powerful in some way, and the inheritance passed to her when her parents (specifically, probably her mother) died. After all, "scent" is basically a metaphor here--only spirit beings can "smell" it; what they're "smelling" is spiritual potency of some sort, that can "feed" them in a way random meat cannot.
Her family probably have historically had some important protective role, and had enemies wanting that to stop, who were responsible for that car "accident". I mean, nobody really thinks that the car spontaneously exploding was really by accident, right?
I have a hunch it was because of that power that her mother managed to say, or convey to her, those last words when any normal human would already have been dead and wouldn't exactly have been audible from under water anyway. Probably also used power to eject her safely from the car.
It's been strengthening since--you can call it puberty, you can call it coming of age, coming into her power, whatever. Maybe if she was able to find out just what that's about and gain control over it, she would be able to camouflage it, as her mother or parents presumably did.
Likely the fox spirit doesn't exactly know about any of that--maybe her monk told her back in the day to keep a special eye on that family, but, holy men tending to be cryptic, never said why.