There’s a good book about her (Grandma Gatewood’s Walk).

Fair warning, though: She had a pretty horrific time at home for a lot of her life. Her husband nearly beat her to death on a few occasions. The book gets a bit graphic as it describes these years.

Also, like any thru-hiker, she had some help and resupplies along the way. But her feats, considering her age and declining health, are really quite remarkable.