How does Kaya's Ghostform interact with Elenda, the Dusk Rose?
You can indeed choose which ability resolves first, but it won't help you.


  Or is the Elenda that returns "different" from the Elenda whose ability was triggered?


Yes, this is exactly what is going on. The rules state:


  400.7. An object that moves from one zone to another becomes a new object with no memory of, or relation to, its previous existence.


There follow nine exceptions to this rule but the situation caused by Kaya's Ghostform isn't one of them.