The power limitation is fine.

My personal issue lies in the gimmick. The superhero gimmick ain't gonna work in this setting. We're constantly in war, the village is not a particularly safe place, even if it is safer than most other places in the world. Being brave and helping people is fine, being schizophrenic is also "fine", it would lead to her being less relied on by well everyone. Putting on a costume and claiming to be a superhero is bizarre and doesn't fit into the setting at all and would only break immersion. Remember that this is 100+ years before the dawn of the actual series. This is a time when everyone is clad in what looks similar to samurai armor and clan wars are always breaking out. World politics are much too shaky and unsafe to justify there being a superhero running around.