Here is a helpful summary of her character and usage in FGO:
She is best used in teams that can provide critical stars to maximize her high critical damage potential. Jeanne d'Arc Alter | TYPE-MOON Wiki | Fandom Joan Alter
As an Avenger, she is a high-damage dealer, often noted for having some of the highest Attack (ATK) values in the game. Key Skills (Leveling Priority): Here is a helpful summary of her character
A younger, comical "Santa" version exists, known as Santa Alter Lily. Boosts critical damage (+50%) and star gathering rate
Boosts critical damage (+50%) and star gathering rate for 3 turns (ideal to level first).
Born from a wish upon the Holy Grail by Gilles de Rais, she represents a twisted version of Jeanne d'Arc seeking revenge. Over time, she develops into her own person rather than just an imitation of her saintly self.