[The story of Megan McMahon is recounted in a book A Place of Healing by Connecticut medical writer, John Dinolfo; however her case is also mentioned in numerous websites including where I picked it up — www.visionsofjesuschrist.com. I have only slightly edited it]:
Dinolfo recounts the story of Megan McMahon, a child from Upper Darby, Pennsylvania, who was born with a potentially deadly eye cancer called bilateral retinoblastoma and was taken to Medjugorje in 1987 — where Megan, by then three, reportedly saw the Virgin herself. Megan was at the one end of the pew, and her mother Jeannie knelt in the center aisle, facing the front, recounts Dinolfo. Seer Marija Pavlovic and others were in a room in the balcony of the church. As Jeannie continued to pray, she was unaware that the nightly apparition had started in the balcony room. Suddenly Megan called out, “Mommy, is that the Blessed Mother?” … Then Megan, with outstretched arms, began to say loudly, in a sing-song voice, “I love you Blessed Mother. I want to kiss and hug you.” So striking was the occurrence that those around the girl began to weep. When asked later what she saw, the girl also mentioned “the big angel,” the color blue, and three or four “baby angels.” When the girl recovered, according to Dinolfo, her surgeon at Philadelphia’s Wills Eye Hospital expressed belief that the force of prayer had “definitely” been at work.