My informant is a native of Brazil and is of Portuguese descent.  According to her, her grandmother, from whom she learned this superstition, was a fervent Catholic and “knew hundreds of saints and their miracles and for every misfortune or mishap there would be some saint to pray to or a superstition to fix it!”  She said superstitions were her grandmother’s specialty.  She recalls of her grandmother: “If it was raining hard with thunder and lightning she would go around the house covering the mirrors: they attract the storm.”
I have never heard any superstition quite like this one, though I have heard others that associate omens with mirrors.  Certainly I have never associated mirror superstitions like this one with Catholicism.  This magic-superstition is probably either taken directly from native lore or is a hybridization of the lore of the Portuguese with that of the native land.