2. Author's Notes
It is described in the Athrabeth Finrod ah Andreth (Morgoth's Ring, HoME vol. 10) how Andreth believes Morgoth to be the source of all evil, death in particular, which she thinks was imposed on the race of Men and not inherent in them from the beginning.
I think her reaction of shock when she meets Cuilendil is plausible, as she supposedly has not encountered mental disability before. The story is meant to show how she learns to see the person behind the affliction.