Saint Isabelle was the daughter of King Louis VIII of France, younger sister of King Louis IX of France (Saint Louis), and older sister of King Charles I of Sicily. Born in March of 1224 at Paris, Saint Isabelle tragically lost her father when she was only two years old. Her mother educated her strongly in Latin and the local language, teaching her how to read tales of chilvalry and religious scriptures. As she began to grow older, she began aspiring for a spiritual life and was learning under the Franciscan order. Pope Innocent IV allowed her to retain some of the friars as confessors by a papal bull in 1254.
She was bethrothed to Hugh XI de Lusignan when the treaty of Vendome was signed in March 1227 but refused to celebrate a wedding because she had decided she would remain forever a virgin, consecrated to Christ. Pope Innocent IV urged her later to marry Conrad IV of German (the son of the Holy Roman Emperor Frederick II) but she too turned this proposal down to maintain her virginity and religious calling.
In 1255, after urging her brother to purchase land for her to form a Sisters minor community when her mother died, King Louis IX (Saint Louis) purchased land in the Forest of Rouvray. The first stone was laid for her community on June 10th, 1256 and Pope Alexander IV gave his sanction on the Rule (composed by Saint Isabelle and a group of Franciscans that included Saint Bonaventure) just a few years later in 1259. This new rule would also later be adopted by French and Italian convents of the Order of Saint Clare. The sisters were allowed to own property and were subject to the Minorites.
Named the Convent of the Humility of the Blessed Virgin, the nuns of the monastery were named Sisters of the Humble Order of Servants of the Most Blessed Virgin Mary. The Abbey locally became known as Longchamp Abbey. Saint Isabelle herself never joined the community, instead staying away from being named abbess so that she could keep her extensive wealth. It is important to note her reasons for keeping this wealth - she used the money and resources to support the growing abbey while giving the rest to the poor who lived around it. It is written that while not visiting the Abbey, she would keep a vow of silence during daylight hours.
Saint Isabelle died at Longchamp Abbey on February 23, 1270 and was buried at the abbey's curch. Nine days later the body was exhumed and showed no signs of physical decay.
Pope Leo X allowed the abbey to begin celebrating her feast day and beatified her in 1521. Permission to celebrate the feast day with an octave was granted on January 25th, 1688 by Pope Alexander. Pope Innocent XII permitted the entirety of the Franciscan Order to celebrate her feast day in 1696 when he formally canonized Saint Isabella.
During the French Revolution, the Abbey was suppressed. Initially the now empty building was set for sale but because no one purchased it, the main building was destroyed in 1794. The land of the Abbey was incorporated into the Bois de Boulogne (a large public park) in 1857. Today her feast is celebrated on February 26th.