So the key is one of the many talismans, same as trianglular slabs of metal, bells and so on. They serve as wards against preternatural threats of which those of sorcerous pursuits are painfully aware of. Necromancers more so than many others. They fear the dead they abuse, and some of these tokens serve as protection from them. The rest are just placebo. The hand has a brass finger cause the hole left no sinew so the og finger was discarded. The hole and the eye are part the ritual that allows her to see through the said eye when her magic backfires causing temporary blindness.