One day whilst she was saying the Rosary...

The daughter of a prince had entered a convent, which was not very fervent, and in consequence, though she was naturally of a good disposition, she advanced but little in virtue. But having by the advice of a good confessor begun to say the Rosary, meditating at the same time on the mysteries, she so changed that she became a model for all. The nuns, however, displeased at her seclusion, did all that they could to make her give up the course she had traced out for herself. 

One day whilst she was saying the Rosary, and entreating Mary to help her in the persecution she underwent, a letter fell before her. On the outside was written, 'Mary, the Mother of God, to her daughter Johanna, greeting.' Inside it she read: 'My beloved daughter, continue to say my Rosary; avoid intercourse with those who do not help thee to live well; beware of sloth and vanity; banish two superfluous things from thy cell, and I will be thy protectress with God.' The abbot, under whose jurisdiction the monastery was, visited it soon after, and endeavored to reform it, but without success. He one day saw many devils enter the cells of the nuns, but not into that of Johanna; for the Divine Mother, before whom he saw her praying, drove them away. 

Having afterwards learnt from her the devotion of the Rosary which she practiced, and the letter she had received, he ordered all the nuns to do the same; and the account says that the convent became a paradise.