Some notes on the armour the figure is wearing, the depiction in the Luc Besson film, and that possibly worn by the historical Jeanne:
She's wearing an incomplete harness/suit of armour. There's no breastplate, only a plackart strapped to the collar. The film shows the arrow piercing her through the exposed mail. Some accounts stated it went as deep as six inches between her neck and shoulder. She also wears no vambraces or rerebraces (upper and lower arm protection).
A couple of things emerged from a scan through various writings this morning.
Jeanne's first suit of armour:
The Dauphin provided her with armour in the spring of 1429 that cost one eighth that of the most expensive armour of the time. At her trial she stated that she had been offered a complete suit of harnois blanc (armour without any embellishment) suitable for a man-at-arms.
This harness was offered to the town of Saint Denis in ex voto after the failed attack on Paris. From that time on Joan wore a suit of armour taken from a Burgundian, the value of which remains unknown. (Source: Olivier Bouzy,"Jeanne d'Arc, Mythes et Réalités").
(Later in film she's wearing a more substantial suit of armour, i.e., the Burgundian armour).
The term “harness” designated the diverse garments of war; to be more precise, one spoke about “of the head” or “of the arm.” Every piece was independent, as attested in the account books of the armories, from whom pieces were ordered separately: a leg harness, an arm harness, a gauntlet, and so on. Jeanne also wore a ...jaseran[a short mail hauberk].... She also wore a brigandine, an armed vest made of a great number of small plates of metal joined by rivets, the heads of which formed a kind og geometric design. The right arm was protected in a lighter fashion than the left, so that a sword or lance could be wielded more freely. The armor of the left arm, by contrast, was folded back to assist in holding the horse’s reins.
We know that the first suit of mail-the blanc harnoys made for her in Tours-had been left be her in the Abbey church of Saint-Denis after the failure of her attack on Paris, and its subsequent history is unknown. We are ignorant of what happen to her second suit of armour. It has been estimated that the purchase of a complete set of military equiment corresponded to two years’ wages for a man-at-arms. It took 8 weeks for the Jeanne’s armor to be made and 600 years later it still takes 8 weeks.
Joan of Arc (Jeanne d'Arc) - Suit of Armour
I came across a note about her armour from Jean de Dunois, which would give an historical reason for it being depicted incomplete.
Dunois (23 November 1402 – 24 November 1468), nicknamed the "Bastard of Orléans", was the illegitimate son of Louis I, Duke of Orléans. He lead the defence of the city during the siege, and joined Jeanne on the campaigns of 1429.
"In the dawn the English came out of their tents and arrayed themselves in order of battle. Thereon the Maid rose from bed, and for all armour wore a coat of mail" (jaseran), says Dunois: she could not bear her heavy plate armour.
The source is the 1908 biography by Andrew Lang,
The Maid of France, Being The Story Of The Life And Death of Jeanne d'Arc (Chapter 13).
This is purported to be the helmet she wore at the Siege of Orléans:
The helmet shown here–a bascinet of the type worn during the 14th and early 15th centuries–is one of these works fraught with historical associations. It is believed to be the helmet that Jeanne d’Arc wore at the Siege of Orléans (1430), one of the turning points of the Hundred Years’ War. It is reported to have hung above the main altar of the church of St. Pierre le Martroi in Orléans (a short length of chain is still attached to its peak): it was considered to have been given as an ex voto by the Maid after she had been wounded at the siege by a crossbow bolt. There are marks of crossbow bolts on the helmet.
Jeanne made use also of a capeline, a steel hat equipped with a wide brim, frequently used when scaling fortifications. But her contemporaries remarked that she often went about with her head bare, which was hardly surprising since military commanders of high rank often wore a simple hood or a hat rather than a helmet.