@MrsEdamame: This is from the Diocese of Phoenix, AZ:
Must Catholics Marry in a Church?
FR. WILLIAM SAUNDERS
Do Catholics have to be married in the Catholic Church? The “straight answer” is simply “yes,” but let’s understand also the “why.”
The “straight answer” is simply “yes,” but let’s understand also the “why.”
In the Sacrament of Marriage, a baptized Christian man exchanges vows with a baptized Christian woman. Before Almighty God, they promise to each other a love that is faithful, permanent, exclusive, self-sacrificing and life-giving. Through marriage, a couple now enters into a new public state of life both in the eyes of the Church and society; therefore, the celebration of the marriage rightfully ought to be public with the vows exchanged before a priest (or other authorized witness of the Church), the witnesses (usually the Best Man and Maid of Honor), and the faithful gathered for the ceremony. (Cf. Catechism, No. 1663.)
Given this basis, a Catholic (either baptized as a Catholic or later entering the Catholic Church after having already been baptized in another Christian denomination) is bound to be married in the Catholic Church. The Church in which one has been baptized and confirmed, receives Holy Communion and professes faith, ought to be the Church in which one is married. Consequently, whether a Catholic is marrying a Catholic or a baptized non-Catholic Christian, the normal expectation is for the marriage to take place in the Catholic Church and for the children to be raised in the Catholic faith.
However, when a Catholic is marrying a baptized non-Catholic Christian, legitimate circumstances may arise when the couple would like to be married in the Church of the non-Catholic. Such circumstances include recognizing a special or long-standing relationship with a minister, or preventing family alienation. In such a case, the couple would complete the regular Catholic marriage preparation. The Catholic party would also attest to his intention of not leaving the Catholic Church and of promising to baptize and raise the children in the Catholic faith. The non-Catholic party would be informed of these promises, attest to understanding these promises and in turn promise not to interfere in their fulfillment. After the preparation and the attainment of these promises, the priest would petition the bishop on behalf of the couple for a “Dispensation from Canonical Form,” meaning permission for the couple to be married outside of the Catholic Church. The Church requires a dispensation because the bishop, as shepherd of the diocese and guardian of the souls, must insure that the couple is prepared as best as possible for marriage and is ready to enter into Holy Matrimony. With such permission, the wedding is valid in the eyes of the Catholic Church. (Cf. Code of Canon Law, No. 1124-25).
So, in the strictest sense of the word, if she wants the marriage considered valid, they must still submit to Pre-Cana and ask for a Dispensation, which are actually a lot more common than they sound.