Goblin livers, their weapons (she'd recognize the same kinda spear that Theo had), as well as small pouches they carry that contain shiny tokens and whatnot. Predictably, goblins don't drop great loot, but if she was trained as a monster slayer, usually she'd make money off of the act of killing a monster, rather than the act of butchering a monster. Adventurers in Oratorio, however, make most of their income from the latter.