The red-head is clearly Est, not Minerva. The three Whitewing sisters.

Incorrect! It's Minerva, not Est, though the confusion is understandable.

-Not Est's hair style (which is a lot more short and boyish).
Est's hair is usually pink, though occasionally it is drawn more reddish, but
-Check the headbands. Paola, Catria (and Est) wear white headbands, hence 'Whitewings'. But Minerva's headband is yellow, which is what this redhead is wearing here.

Now, why is Est missing from the picture? I don't know. My guess is that the artist wanted to draw busty characters, and Est isn't usually drawn with large boobs? That's the only explanation I can think of.