I would prefer
Leda.
I have nothing against female names ending in -o in general, but
Leto unfortunately has been sort of cemented in my mind as a male name by the characters in
Frank Herbert's
Dune series. The father of
Paul, the hero of the first book in the series, is
Duke Leto Atreides, and
Paul names his son after his father. In later books in the series, that son becomes Emperor
Leto. It may be sad, but I'm afraid these days many more people in English speaking countries will be familiar with these male Letos from
Dune than will be familiar with the original female mythological character.