Byrne was one of 15 people who witnessed an unusual sight at the gable end of the church on 21 August 1879, later the site of the Knock Shrine.
Byrne identified the third figure of Saint John the Evangelist, as he bore a resemblance to a statues at a church in Lecanvey, near Westport, County Mayo.
[4] Byrne went to nearby houses, and brought the rest of the group of 15 to witness the apparition, including her siblings, Dominick and Margaret, and her mother.
The parish priest, Archdeacon Bartholomew Cavanagh, refused to attend the site as he did not believe his housekeeper's claims.
In 1880, on the first anniversary of the vision, Byrne took part in a commemorative procession carrying a banner of the Virgin Mary.