I believe the song “Faith of our fathers” is refering to the faith handed on to us by the Fathers of the Church. For this reason the ‘new’ verse about faith of our mothers makes no sense. The only mother we have is Mary.
Glory to Jesus Christ!
Yes, we have only one Mother, the Theotokos, just as we have only one Father, God. As there are a number of “fathers” of the Church, we also have a number of “mothers” of the Church.
Check out The Forgotten Desert Mothers, by Laura Swan.
In fact, Aquilina devotes the last chapter of his book to what he informally calls the Church “mothers.” An excerpt:
"… to many modern minds it raises the question: Were there “Mothers of the Church”?
To which the answer is: yes and no.
We possess very few writings by women from the ancient world … women faced fewer educational opportunities than men …
This does not, however, mean that women were passive members of the Church … women made up a disproportionate number of converts … women played active roles in the running of the Church …
Women made up a great number of the early martyrs, and their stories and their cult of honor were often more popular than those of their male companions …
Women were just as active in the monastic movement. The many collections of “Sayings of the Desert Fathers” actually include proverbs by women ascetics …
Their contemporaries honored these women as maternal figures. The Church has always honored them as saints. There is no custom of calling them “Mothers of the Church,” but there is no reason why individual Christians might not revere them as such."
Aquilina then goes on to excerpt some of the writings of Perpetua, Syncletica, and Egeria.
Not that any of this justifies forcing a “faith of our mothers” into a traditional hymn!