I may be wrong (frequently happens), but I don’t think the priest can give her permission to use the church, if it is consecrated. She maybe could use the parish hall. Maybe the VFW could rent their hall to her?
She has serious problems anyway if she doesn’t want a priest to do the marriage, or witness it. How does she get by Diocesan requirements for marriage prep? Or doesn’t she care about that, either?
I think you are correct. A parish Pastor may not give such permission, and I doubt a Bishop would since the Sanctuary is consecrated in all Catholic Churches.
CCC " 1183 The tabernacle is to be situated "in churches in a most worthy place with the greatest honor. The dignity, placing, and security of the Eucharistic tabernacle should foster adoration before the Lord really present in the Blessed Sacrament of the altar. "
CCC " 1383 The altar, around which the Church is gathered in the celebration of the Eucharist, represents the two aspects of the same mystery: the altar of the sacrifice and the table of the Lord.
This is all the more so since the Christian altar is the symbol of Christ himself, present in the midst of the assembly of his faithful, both as the victim offered for our reconciliation and as food from heaven who is giving himself to us.
For what is the altar of Christ if not the image of the Body of Christ?" asks St. Ambrose. He says elsewhere, “The altar represents the body [of Christ] and the Body of Christ is on the altar. we may be filled with every heavenly blessing and grace…”
CCC " 2120 Sacrilege consists in profaning or treating unworthily the sacraments and other liturgical actions, as well as persons, things,
or places consecrated to God.
Sacrilege is a grave sin especially when committed against the Eucharist, for in this sacrament the true Body of Christ is made substantially present for us."