[@Rhiannon]
The Eaten themselves only have enough magic in them to create potions and maybe cast a couple low level spells. Maybe since Energy Witches have spirit stuff and the curse is partly spiritual in nature they can temporarily banish the invisibility. I imagine that the Eaten's magic is basically like the coals after a fire, the heat is still kinda there but it would take some work to "light it up" so to speak. If an Eaten dedicated themselves to developing their magic they might be able to get the majority of it back, but it would take a couple decades at least. Anyway I'll get a CS up here sometime soonish. Might have to steal some of these CS formats, they are pretty good.