Sothis (sopdet in greek) represents the Dog Star, Sirius. After research, a giant dog atop a meteor seems to represent Sothis - so the main form, a slightly more canine one, was decided.

In the first cutscene, the glowing shape kind of looks like a wing, or a bird tail so... the tail and wing vibes were done!

Colours were decided easily:

the giant lady is sothis, so I'm using her colour scheme (particularly the wing colour), and the green, pink, and gold from sothis' young form.

Completely randomly, I decided the breath weapon/ fire would be the rainbow transitioning colours from the first cutscene.

Anyway! That was an overly long description of why I doodled a dragon like that.