you need to deploy this unit in your formation: http://mononohu.gamerch.com/%E7%A8%B...B8%80%E9%89%84
unfortunately, this is one of the most fucked up star requirements early on (I myself didnt get her until after couple of weeks of gameplay), but luckily you only see like 1 or 2 of this one early on, and none after. I ended up keeping 1 copy of her either way