I think there are a few hints - for example, the mythical Cassandra and Helen were also (non-mutual) twins, and putting a "Cassandra" and "Helen" on a Greek isl

I think there are a few hints - for example, the mythical Cassandra and Helen were also (non-mutual) twins, and putting a "Cassandra" and "Helen" on a Greek island (and maybe also in some sense "Paris") you're definitely being primed to think in that direction. I would need to watch it again to see if there's something more blatant as she shows up. My nitpick is that Peg felt mostly extraneous - the main plot beat conversation with Peg could've been a conversation with Birdie directly. (And Derol is already present as the extraneous-for-the-sake-of-it element.)