Ok so one of the things about Sin-Eaters is that they can get power from "mementos" or artifacts imbued with death energy, and when the mementos are small enough they really like to incorporate them into clothing and jewelry and generally just bling themselves out with morbid crap.

And also between Ammond's personal tastes and the interests of her Geist, a disproportionate amount of the mementos she carries are the result of traffic accidents and therefore tend toward being like hood ornaments and tail-light bulbs and other assorted bits of shiny metal or glass.

So what I'm saying is how long before this kinda-mostly-human girl hanging around your weird Bagheera friend starts noticing that her mystical charms are going missing.