Eldest of five children of Giulio Mastena, a grocer, and Maria Antonia Casarotti, an elementary school teacher. Raised in a pious family; one brother was a priest, another tried to be, and a sister became a tertiary. Received First Communion on 19 March 1891, during which she made a private vow of chastity. Received Confirmation on 29 August 1891. Feeling a call to religious life, she tried to take the veil at age 14, but was considered too young. At age 17 she joined the Institute of the Sisters of Mercy in Verona, Italy. On 24 October 1903 she made her profession, and received the name Sister Passitea of the Child Jesus.
She began work as a teacher in 1907. In 1908 she and three other sisters was sent to Miane, Italy to found a new house andschool; Sister Passitea served as the superior and headmistress. Worked there for nineteen years, teaching and running the house business; noted for her help and support of the families with sons fighting in World War I. In 1927, feeling a call to a different spiritual life, she entered the monastery of San Giacomo di Veglia, and on 2 June 1927 joined the Cistercians, taking the name Maria Pia.
In the cloister she was known for strict adherence to the rules, and devotion to the Eucharist, to the Passion of Jesus, and to his Holy Face. However, she soon began to realize that the cloistered life was not for her, and she returned to service as headmistress of the school in Miane. She was transferred to schoolsin Carpesica, and then to San Fior. In 1930 in San Fior she founded the Institute of Sisters of the Holy Face with the mission to "propagate, repair and restore Jesus' gentle image in souls". On 8 December 1936 the Institute was canonically erected as a diocesan Congregation, and the first ten members made their perpetual vows, and Mother Maria Pia was appointed Superior General, a position she held the rest of her life.
