Warning if you haven't read all of Stormlight Archive, and Mistborn Why, also you might not want to read this
In Stormlight Archive it says that Shallan can suppress her stormlight, and in mistborn smokers hide the pulses of investiture, and stormlight is just a different form of investiture, I would think that due to Shallan's childhood she definitely had enough trama to snap and be able to burn copper, although it doesn't say she senses a reserve I imagine that it just would be hidden by the stormlight, also could she be using stormlight to power her allomancy
Edit please tell me your thoughts on my theory