Not, of course, that "martyred" is the word we are supposed to use to describe what happened to her. When the Church finally got around to canonizing Joan in 1920, (the process nearly being derailed a number of times, including by a rather vigorous advocatus diaboli who was rather concerned over whether Joan's squire might have seen her naked breasts when he was arming her, or treating the wounds she suffered in battle) she was entered into the calendar of saints as "virgin" not as "martyr" (the only two paths to sainthood for women.)
It was the Church, you see, that burned her.
Joan has been my favorite saint for as long as I can remember. Brave, articulate, and fierce, she was a girl with a sword who got things done - the kind of girl I wanted to be. But her story was one I knew so well that the details ran together. Then, at the beginning of my career in legal academia, I wrote an article called "Lex and the City" (pseudonymously as Gil Grantmore, and yes, for those of you bored completists out there, I'm sure you can find it on the internet) about the first amendment right to freedom of speech inherent in personal dress. It was then I discovered that the heresy that Joan had been burned for was wearing men's clothing.
Seriously. After a trial that went on for months, wherein Joan was assaulted, poisoned, threatened with more explicit torture, was forced - illegally - to act as her own advocate while being questioned by upwards of 50 members of the Church hierarchy at once, the only heresy they could find her guilty of was that of wearing pants. I didn't realize it at the time, but my dissertation was born in that moment.
Once I began researching her more seriously, spending months, and then years reading the transcripts of all of her trials - The Trial of Condemnation, the Trial of Rehabilitation (which cleared her of all charges, twenty-three years too late), and the Trial of Canonization - I became more and more impressed with her bravery and grace. And I understood, more and more, why this young women - articulate, intelligent, a girl with a sword who got things done - struck such terror in those in power.
So much terror that when the English captured her, the French abandoned her to death, rather than paying a ransom, such as was commonly done for prisoners of war of her status. So much terror that, aside from housing her in a men's military prison, rather than in a women's ecclesiastical one, her interrogators, theoretically men of the Church, asked her if she might lose her powers if she lost her virginity. Rape was a weapon, even then. So much terror that they burned her alive.
If you want to read more about her, I highly recommend Joan of Arc: Her Story by Regine Pernoud, one of the greats of Jehannine scholarship. Or George Bernard Shaw's Saint Joan. All of the best lines truly are hers.