These places were not convents, but beguinages, and the women in them were not nuns, but Beguines. In these communities, which sprang up spontaneously in and around the cities of the Low Countries from the early 13th century, women led lives of prayer, chastity and service, but were not bound by vows. They could leave; they made their own rules, without male guidance; they were encouraged to study and read, and they were expected to earn their keep by working, especially in the booming cloth trade. They existed somewhere between the world and the cloister, in a state of autonomy which was highly unusual for medieval women and highly disturbing to medieval men.Rest in peace.
UPDATE: Obituary from The Daily Telegraph (UK).