After nine days her body was exhumed, when it showed no signs of decay, and many miracles were wrought at her grave.
In 1521 Leo X allowed the Abbey of Longchamp to celebrate her feast with a special Office. On 25 January, 1688, the nuns obtained permission to celebrate her feast with an octave, and in 1696 the celebration of the feast on 31 August was permitted to the whole Franciscan Order. The history of the Abbey of Longchamp had many vicissitudes.
In the new rule Urban IV gives the nuns of Longchamp the official title of "Sorores Minores inclusæ, which was doubtlessly intended to emphasize closer union with the Order of Friars Minor .
After a life of mortification and virtue, Isabella died in her house at Longchamp on 23 February, 1270, and was buried in the convent church.
Clare, Louis IX began in 1255 to acquire the necessary land in the Forest of Rouvray, not far from the Seine and in the neighbourhood of Paris.