There is an earlier discussion on this forum about beings switching off their MR based on MIght.
Suppressing the MR granted by True Faith is similar.
What is the general relation of the character with True Faith to Magic? Would she even consider abandoning Divine protection against it?
If she has a "real high" True Faith (see RoP:D p.61f Embodying the Light), she might pray for a Miracle instead (see RoP:D p.60f Miracles, perhaps RoP:D p.87 Invoking a Saint and The Church p.13 The Benefits of Devotion).