The Phoenix theory.

The Phoenix Theory:

This theory mainly goes towards the idea that Felicia is the other Phoenix that Twig used to hang around with, not only that but she is also the same Micro-Phoenix that used to be owned by Onas Dulin's Sister.

The reason for this theory is that /u/SendaiNex revealed that a divine source will be needed to resolve Felicia's Plotline. This lead to a lot of people to question the coincidence between the events of Dulin's death and Felicia's arrival happening around the same time.

A line of thinking began thinking that Felicia's return was a form of wish fulfilment. (Which also lead to the Construct Theory being created)

Until his death, Onas prayed  to the god Desna for the return of his sister (Something revealed while the party was off-screen). A common consensus with this theory was that it must of been the god Desna who fulfilled his final wish bring his sister to life.

The more interesting relationship between Twig and Felicia (the same reflections visions and the fact that Twig adored Felicia even though she was humanoid) caused the Phoenix Theory to be created.

In short, Desna turned the other Phoenix into Felicia as it would have the most "memories" of Dulin's Sister and would be able to emulate her to allow Leithia to live on after Onas's death. This would explain why Felicia would get visions of being in the sky and also recognise the family crest while not being to remember her former life.