Laura described Mary as being very sweet and good as a child, with beautiful golden hair that Laura greatly coveted. At the age of 14, however, Mary became very ill and had a stroke, resulting in blindness. Laura became "eyes for Mary", describing everything she saw for her blind sister.
From 1881-1889, Mary attended the Iowa School for the Blind in Vinton, Iowa, because no education for the blind was available in Dakota Territory. She then returned home to De Smet, South Dakota, where she lived with Pa and Ma. She never married. After Ma's death in 1924, Mary lived with Grace and her husband until her death on October 17, 1928, while visiting Carrie's home in Keystone, South Dakota.
Mary's Braille Bible, slate, and other books, beadwork she made following her blindness, her gloves, and a nine-patch quilt she made as a child are all on display at Rocky Ridge in Mansfield, Missouri. Other items belonging to Mary are housed in the Ingalls home at De Smet, South Dakota.