Did Monet's Yuki-Yuki fruit turn her into a harpy? Did Monet's Yuki Yuki fruit turn her into a harpy or was she part of Caesar's experiments that turned her into a harpy?
It was Law who turned her into a harpy. The Yuki Yuki no Mi had nothing to do with it. Much like the pirates who lost the use of their legs became centaurs, it was Law who turned Monet into a harpy; the only difference is that the change happened willingly in Monet's case; the reasons weren't explained as far as I can remember, but it was most likely to make her stronger.