Swan Lake is a very strange ballet.....I also wonder how can Siegfried fall in love with a bird(the Swan) and take him to a party to introduce she/it to his mother:"Mum that's my new girlfr....ehm....bird.Can I marry her?"....hahahahah!!!!and then,if at night Odette gets back to being a woman,why does she dance and behave as a Swan in the second act,when she is supposed to meet her prince as a woman ?i don't think there is any aswer to these questions...
Siegfried is in a strange place when he leaves the palace/palace grounds (or in Kudelka's version, the local saloon). He's about to be forced into a decision he doesn't want to make, and he thinks there's something else out there. He's in the dark forest in the middle of the night, and he's up for something different.
Odette is an exotic. She's not a swan physically, literally, but like anyone else who's not an actor or an actress, you can dress them up to look one way, even a way that is part of themselves, but the rest of them is still in another world. (Hence the swan movement.) Look at old photos of immigrants who are in formal dress of their new countries and how half still in the world from which they came. They still move the same way.
And while Odette may not have made much of an impression at the party -- skittish, sad, withdrawn, however regal -- Odile makes a grand entrance in a little black dress (originally red and gold, no?), is as sociable as can be -- convinces Mama to give her a chance, with the help of Von Rothbart, charms the pants off of everyone at the party, and speaks to the Prince on a hormonal as well as spiritual level. (Odette would make a horrible Princess; she'd be a recluse like Tsarina Alexandra, and look how that turned out.) What more could a Prince want?
Odile shines under bright lights, in public. Odette under moonlight, in an intimate setting.
"Swan Lake" is about psychological truth, not literal truth.