So it seems like Saki really has a ponytail, even in her official art. I didn't notice it at first and thought it was just short hair (like Aya's).

That's pretty nice since it makes her stand out more. Ponytails are kinda rare in Touhous, and the only ones that come to mind are Futo and Yorihime (but I may be forgetting others).

In her case, a literal ponytail no less.

It's hard to tell in her official art between the angle, the hint of her tail, and her wings all sharing the same coloration. I thought it was part of her wings honestly.