Probably the Monster Hunter fanboy in me talking, but it kind also looks more like Dragon-type than Fairy due to the colorization. Although, if I were to put a top guess, I'd say it looks like a water-type as it's hair looks like mist and fog.
That's more due to lighting, though.
https://en.wikipedia.org/wiki/KelpieI’m interested in the possible lore on how Ponyta came to be (assuming) fairy in the Galar region. What happened to their fire and why?