She was a wash-out, something about the augmentation procedure made her unfit for battle-- or that's what I always heard, did the story not actually say that? Assuming she was, there were any number of possible issues; the wash-out in Conversations From the Universe talked about continuous, painful surgeries, well into the war. Anyway, when the attack on Earth started, I'm sure she picked up a gun one way or another, along with everyone else that could use one.