Originally, Tiki in Divine Dragon form goes from the white look in book 1 to the golden feathery look in book 2. So, it seemed to be just her form changing due to her getting more powerful. But then New Mystery just reused Shadow Dragon's sprite. Then Awakening had a completely new form, also shared with Nowi. Heroes then had the silver Shadow Dragon design and kind of retrofit the others into it - adding some details of Awakening's version onto it for adult Tiki, and later versions of Tiki got a golden color swap, but without feathers.
Warriors though actually brought back the FE3 Book 2 Divine Dragon design as Tiki's promote look, going from white/gray to yellow, but also gave her a modified tiara. Engage only uses the book 2 design, although modified again - giving her white feathers on the wings and "hair" on her face, keeping the tiara like in Warriors, but with a different shape (the ones on the chest were already there).
So... yeah.. they seemingly can't decide at all even Tiki's specific dragon design. So, it's not surprising there's no consistency with a separate character (although being from different worlds is enough of an explanation). The original intention seemingly was her dragon form changing as she got stronger though.