Late medieval Christians were pretty much obsessed with legendary female saints of the early Church who almost certainly didn't exist, like Catherine of Alexandria and Margaret of Antioch. But this was not the case for saints of their own time. Joan of Arc, in fact, might be the most-attested peasant of the era. You can find a collection of the most important primary sources in translation here.

To hit some of the highlights:

• During her short military/prophetic career, her reputation was already great enough and secure enough (in France, at least) for humanist author Christine de Pisan, a champion of women's abilities in the literary "querelle des femmes", to use Joan's deeds to her advantage.

• There are some surviving letters that she dictated--during the trial, she was questioned about her letter-writing

• We have records of her actual trial involving named, high-powered Church officials

• At the "rehabilitation" trial (after she was already dead), numerous witnesses testified to her life and deeds

If you're interested, Regine Pernoud's Joan of Arc: Her Story (and the French it's translated from :P ) stick closer to the original source record in reconstructing Joan's life than traditional biographies--basically, they go through the sources chronologically, instead of events in her life.