I don't know what their official DnD categorization is, but they are completely sentient and literally just a female elf nude body with bird-like hands, feet and wings.

So to me they're more like a tribal half-humanoid, similar to Centaurs who are half-human/half-horse or Mermaids who are half-woman/half-fish. A monstrosity to me is something like a Minotaur, which has no humanoid characteristics considering it is an upright walking bull on steroids.