Mary Katharine's name was spelled "Katharine" in her parents' Bible record. She was sometimes called Mary Kay, most often went by "Katharine", but she was called "Katie" by her family members. She was a dress designer. She died of leukemia.

Yes, she went by Katie; she was 8 years older than Mom ‏[Marjorie]‏ and Aunt Margaret. She more or less raised the girls; grandma Ella was busy taking care of her husband. Aunt Katie was very talented. One of the many things that she could do was design and make, for herself and for others, cocktail dresses with her power machine.
Source: This information was sent by facebook private message to author from Susan ‏(Jenkinson)‏ Caldwell, 23 Dec 2018.