This is what I found:

In May 1802, excavators in the ancient Catacomb of St. Priscilla in Rome came upon a well-intact shelf tomb sealed with terra-cotta slabs in the manner usually reserved for nobility or great martyrs. The tomb was marked with three tiles, inscribed with the following confusing words: LUMENA/PAXTE/CUMFI. However, if the first tile is placed last and the words are separated properly, the sentence becomes: Pax tecum, Filumena, which is, "Peace be with you, Philomena."

Also inscribed on the tiles were several symbols: a lily, arrows, an anchor and a lance, which would appear to indicate virginity and martyrdom. Inside the tomb there was discovered the remains of a girl between the ages of twelve to fifteen years of age, along with a vial or ampulla of her dried blood.

The relics (bones and blood vial) were exhumed, cataloged, and effectively forgotten since there was really nothing known about the young girl.

Then in 1805 the first miraculous occurrence came about at the time Canon Francis de Lucia of Mugnano, Italy was in the Treasury of the Rare Collection of Christian Antiquity (Treasury of Relics) in the Vatican in the storage vault where the relics of Philomena had been placed. When he reached the relics of Saint Philomena he was suddenly struck with a spiritual joy, and requested that he be allowed to enshrine them in a chapel in Mugnano.

After some very delicate negoiations and several heated disagreements, settled by the cure of Canon Francis following prayers to Philomena, he was allowed to transport the relics to Mugnano. This was unusual as relics were seldom (almost never) releasted to parish priests.  Almost right away, Miracles began to be reported at the shrine including cures of cancer, healing of wounds, and the Miracle of Mugnano in which Venerable Pauline Jaricot was cured of a severe heart ailment overnight.

After being miraculously cured, Ven. Pauline Jaricot insisted that Pope Gregory XVI begin an examination for the beatification of St. Philomena, who was to become known as the "wonder worker". After hundreds of other miraculous cures, she was beatified in 1837.

Eventually, Philomena became the only person recognized as a Saint solely on the basis of miraculous intercession as nothing historical was known of her except her name and the evidence of her martyrdom.

• Pope Leo XII granted permission for the erection of altars and churches in her honor.
• Pope Gregory XVI authorized her public veneration, and named her patroness of the Living Rosary.
• The cure of Pope Pius IX, while archbishop of Imola, was attributed to Philomena; in 1849, he named her patroness of the Children of Mary.
• Pope Leo XIII approved the Confraternity of Saint Philomena, and raised it to an Archconfraternity.
• Pope Pius X raised the Archconfraternity to a Universal Archconfraternity, and named Saint John Vianney its patron.
• Saint John Vianney himself called Philomena the New Light of the Church Militant, and had a strong and well-known devotion to her.
• Others with known devotion to her include Saint Anthony Mary Claret, Saint Euphrasia Pelletier, Saint Francis Xavier Cabrini, Saint John Nepomucene Neumann, Saint Madeline Sophie Barat, Saint Peter Chanel, Saint Peter Julian Eymard, Blessed Anna Maria Taigi, and Venerable Pauline Jaricot.

May 25th is the anniversary of the finding of the Relics of Saint Philomena in the catacombs of St. Priscilla in Rome 1802. This is a solemn day of prayer at the Sanctuary and a popular time for pilgrimages.

The grandest festivities and processions for Philomena take place in August and last for five days. This includes the liturgical feast within the diocese of Nola of the Translation of the Holy Relics from Rome to Mugnano del Cardinale on August 10th. Thousands of devotees attend annually and the Miraculous Statue, covered in gold donated jewelry is carried through every street in the town.