If you've never read my work before, I cover this topic in
my theory of the Lunarian's history, specifically near the end of the first post.
We know that Monet has been interested in birds since childhood on the basis that her one childhood depiction has her carrying a textbook on birds, which gives just enough of an excuse that if we never learn the full story, most people would accept that she just likes birds. In my theory, though, I suggested that she may have met a Lunarian in her youth, explaining her interest in both ornithology and astrology. Since she knew that the Lunarians were either critically endangered or functionally extinct, Monet may have been motivated to become a harpy in an attempt to emulate the Lunarians.