Satsuki |皐月| yes i would say its Aza on the cover. During the book, they commented on the eyes Aza had, and the cover model had the eyes like her. It could be Ivy, but i doubt it. Also, Aza has the mirror in hand, and she was interested in it during the book. So in short, yes I'm sure it's Aza.
PALACEHERO It is because in the book, it says she has htun (black) hair and pale lips. She also said her eyes were her only attractive feature. That is most likely Aza on the cover.