The book Our Generations of Legacy: A Memoir has a section that talks about her. 

It mentions that she was born in Burke County, North Carolina, and married in 1888, which would've been when she was 13. If she actually married this early, then it would be a strong indication she was at least close to her claimed age, although it's possible this year could've just been derived from the knowledge that she married at 13 without the actual date ever being clarified or proven. Here are a few excerpts that might be helpful: 

"The cry of a baby at its birth is a festive and wonderful sound to hear no matter where you are, and it's a sound people have heard for many years. What joy a newborn baby is indeed, and on March 13, 1875 in Burke County, North Carolina, the Causby family heard the cry of a unique baby who would one day grow up to be a role model for the many generations following hers. This gift, inspiration, and blessing was my Great-Grandma Watts.

All throughout her childhood, she and her family lived in the South Mountains of Burke County, North Carolina on a family owned farm-a great place to reside. She worked with her three brothers and two sisters from dawn till dusk most days making sure the garden was in good shape- digging up roots and weeds-and picking the herbs and vegetables afterward. They picked everything they were able to as soon as it was ripe and ready. What they could spare, they took down to the market and sold or traded to buy coffee and/or salt. These supplies were some of the most immediate materials they sought, and they didn't have a need to purchase other products because her family grew or made everything else on their farm.

Grandma Watt's family mainly stayed home, tending to their daily chores which required patience. Other than that, they went to church, brush arbor meetings, and school. Grandma Watts attended a one-room schoolhouse, but never achieved her full education because she was needed for work as an extra hand on their farm.

Lack of education didn't have a major effect on her life, and the older she grew, the wiser she became. She developed a strong common sense. She shared her wisdom and gave advice on life better than anyone with a degree ever could. However lack of education did affect the way she read, wrote, and spoke. According to her, this didn't bug her too bad because she had all she needed-good looks[...]

[...]In 1888 Martin Watts took Grandma's hand in marriage, and they made a vow which they kept for fifty-five years. During this wonderful, but intense time together, they conceived six boys and six girls[...]

[...]One of Grandma's children was born with Down's Syndrome, and at that time medical experts didn't know as much about this condition as they do now. All they knew was he looked and acted differently from everyone else. His name was Julius, and my great grandmother loved him dearly. One thing I adore about Grandma and Julius is their relationship. Grandma determined in her herself, making it her priority, to take care of him no matter what circumstances arose, and did so until his passing in June of 1982. They were close to one another, close as bread and butter, and Julius loved his mom just as much as she loved him.[...]

Well, her marriage record to Martin Watts says that they married in 1897. So she was likely a young teenager since the 1900 census supports 1882. They probably adjusted her marriage date to fit her age claim.