Suggest she read the Catechism section on marriage, it begins at 1601 and you can read it on line here:
scborromeo.org/ccc/p2s2c3a7.htm#1601
Section on the actual ceremony
1621 In the Latin Rite the celebration of marriage between two Catholic faithful normally takes place during Holy Mass, because of the connection of all the sacraments with the Paschal mystery of Christ. In the Eucharist the memorial of the New Covenant is realized, the New Covenant in which Christ has united himself for ever to the Church, his beloved bride for whom he gave himself up.121 It is therefore fitting that the spouses should seal their consent to give themselves to each other through the offering of their own lives by uniting it to the offering of Christ for his Church made present in the Eucharistic sacrifice, and by receiving the Eucharist so that, communicating in the same Body and the same Blood of Christ, they may form but “one body” in Christ.122
1633 speaks mixed marriages and the of the disparity of cult.
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Difference of confession between the spouses does not constitute an insurmountable obstacle for marriage, when they succeed in placing in common what they have received from their respective communities, and learn from each other the way in which each lives in fidelity to Christ. But the difficulties of mixed marriages must not be underestimated. They arise from the fact that the separation of Christians has not yet been overcome. The spouses risk experiencing the tragedy of Christian disunity even in the heart of their own home. Disparity of cult can further aggravate these difficulties. Differences about faith and the very notion of marriage, but also different religious mentalities, can become sources of tension in marriage, especially as regards the education of children. The temptation to religious indifference can then arise.