Interesting, I never heard of that title for Our Lady.
St John of Matha wasn’t the first man to set out freeing slaves in this way.
St Eligius (Elias) 588-660 was noted for this work...
Religious men and monks also flocked to him and whatever he could collect, he gave to them in alms or gave for the ransom of captives, for he had this work much at heart. Wherever he understood that slaves were to be sold he hastened with mercy and soon ransomed the captive. The sum of his captives redeemed rose from twenty and thirty to fifty and finally a hundred souls in one flock when they were brought in a ship, of both sexes and from different nations. He freed all alike, Romans, Gauls, Britons and Moors but particularly Saxons who were as numerous as sheep at that time, expelled from their own land and scattered everywhere. If it should happen that the number of people for sale outweighed his means, he gave more by stripping what he had on his own body from his belt and cloak to the food he needed and even his shoes so long as he could help the captives. And often it was pilgrims of Christ that he rescued. Oh, daily did he wish to be a debtor that his own debts might be forgiven? Daily did he not rip golden bracelets, jewelled purses and other gold and gems from himself so that he might succor the miserable? Let me briefly comprehend how many multitudes of captives over successive periods of time he freed from the harsh yoke of dominion and how much alms he distributed to people of both sexes, diverse churches and monasteries, though no orator, however studious or eloquent, could tell the tale. Standing directly in the presence of the king, redeemed captives threw the denarius before him and he gave them charters of liberty. To all of them he gave three choices: since they were now free, they could return to their own country and he would offer them what subsidy they required; if they wished to remain he would accommodate them willingly and include them not among his servants but as his brothers; and, if he could persuade them to embrace the venerable life of monks and take the cloister of a community, honoring those marked for the lord, he would supply clothing and whatever else was needed for their care.
https://sourcebooks.fordham.edu/basis/eligius.asp
There’s a very famous painting depicting St Eligius ––
A Goldsmith in his Shop –– by
Petrus Christus. It’s located in the
Met Museum, New York.
A while ago I did some research on the painting’s iconography after coming across an art historian’s published a paper attempting to debunk the St Eligius connection. He was mistaken, simply because he failed to pick up on the strong Christian message in the painting. Uncovered a lot more besides. All at
Resurrecting St Eligius at this link:
https://www.arnolfinimystery.com/resurrectingsteligius