The letters of Bl. Jordan to Bl. Diana remain some of the most beautiful examples of holy friendship which characterizes the Order to this day. We have none of Bl. Diana's letters, probably because Bl. Jordan destroyed them all while traveling.
You can read the letters of Bl. Jordan here.
LOVE BETWEEN THE SAINTS
The preface of the volume To Heaven with Diana contains a beautiful meditation written by the great Fr. Gerald Vann, OP. You can read it here.