To date, nobody has managed to beat Ginga as the most sensibly armored girl in Nanoha yet.
And yes, she holds that title with only a torso plate. I know magic substitutes for the real thing, but it's still pretty sad. Fairy Tail has shown that armor can be awesome on girls, and I'd like to see more from the people who practice the style that used to have it as one of their main perks.