The following is taken from Croatian Conference of Bishops website:

Born in the mountains overlooking the old town of Kotor to the Kosić family, at her baptism she received the name of Katarina. She lived as a shepherdess, brought up in a commendable manner by her pious mother. Katarina asked her parents to allow her to go to Kotor so she could be a better servant of God near the cathedral consecrated to St. Tryphon [sv. Tripun] and other churches. Her mother granted Katarina's wish only after her father's death. In Kotor, she made her first confession and took her First Communion. Katarina worked as a servant for the well-known Buća family. An exemplary girl, she learned to read and write during her free time. In addition to her mother tongue, she read religious books in Latin and Italian, especially the Holy Scripture. In 1513 on Good Friday, in the Cathedral of St. Tryphon, while participating in the Holy Mass and listening to an ardent sermon, she decided to devote herself to contemplation of the Passion of Christ, prayer, penance and good works.

Initially, she lived as a penitent next to the Church of St. Bartholomew [sv. Bartol]. On January 25, 1515, she became a Dominican nun of the Third Order, taking her vows and assuming the name of Hosanna [Ozana] in honor of the Blessed Hosanna of Mantua who died in 1505. When an earthquake destroyed her modest home, in 1521 she moved next to the Church of St. Paul [sv. Pavle] and began a strict, penitential life. In a tiny room, Hosanna spent the next forty-four years in prayer, penitence and experienced a mystical union with Christ.

Sensing the approach of the end of her life, she asked to be brought into the Church of St. Paul. Here she received the Holy Sacraments from her Dominican confessor Fra Tomo Bosco. She wanted them to read her the description of Christ's Passion from the Gospel of John. At the age of 71, she surrendered her soul to God after 52 years of exemplary penitential life. Her incorrupt body was in the Church of St. Paul until 1807 when the French Army transformed the church into a warehouse. Her body was then brought to the Church of St. Mary. The people venerated her as a saint and appealed to her for their needs. In 1905, the process for her beatification began in Kotor and was successfully completed in Rome. In 1927, Pope Pius XI approved her veneration.

In her room, the Blessed Hosanna constantly lived in God's presence. A skilled embroidress, she embroidered a corporal that is preserved in the Kotor Cathedral. She worked for many ladies in Kotor and the environs. All payment for her labors was distributed among the poor. Owing to her efforts, the girls who joined the Dominican Third Order began to live a communal life in the Monastery of St. Paul, which the Dominican Brothers turned over to them. The monastery was abolished by the French authorities in the early 19th century.

Ozana was particularly devoted to the Passion of Christ, the subject of her faithful contemplation. She prayed and sacrificed constantly for the souls in purgatory. She received Holy Communion three times a week, which at the time was considered too often. Her days were spent in fasting and other penitential acts. The people of Kotor called her "the trumpet of the Holy Spirit" and the "teacher of mysticism." Common people and the nobility, city fathers and bishops alike came to her for advice. She interceded particularly for peace in the town and among feuding noble families, common people and the gentry, as well as individual citizens. Therefore, she was called "the Virgin Reconciler" and the "Angel of Peace." People from her village were always gladly welcomed and urged to live an upright Christian life. Many consider her to be an Apostle of Christian unity and a patron of the ecumenical movement.

In addition to St. Tryphon, the citizens of Kotor venerate her as their patroness. During earthquakes, the plague and other disasters she saved the town, especially on August 9, 1539 when Khair-ed-Din Barbarossa, the Turkish corsair (pirate), conquered Herceg Novi and attacked Kotor with his sailors. The Blessed Hosanna encouraged the citizens to fight heroically to prevent the town from falling into enemy hands. After a siege of several days, the Turkish fleet had to retreat without succeeding in its mission. This victory is commemorated by a Latin inscription over the town gates.