is it possible this lady actually says she is a member of a secular Franciscan order, a spiritual group for lay people? It is also entirely possible that she has joined one of a number of orders who accept older people, even those who have been married or have raised families. Typically the order would insist there are no minor children. Strictly speaking if they are living in “the world” they would not be called nuns (who live in cloisters or convents) but sisters, but that distinction is not observed much any more. different orders have different requirments, depending on the mode of living they require, the charisms of the order, the type of work the members will be doing etc. All orders have some required period of formation and education that addresses both the spiritual growth of the individual, their preparation for community life, and education to fill whatever tasks will be asked of them. A divorced Catholic would normally be required to have a decree of nullity before being considered as a candidate for a religious order (or for ordination).