Mabel is really a niece of James and Mattie, but I do not know for sure who her birth parents were. She was already living with them the first time she appears in a census. The most likely candidate is James’ brother Frank, since his son Allie was also living with James and Mattie in the 1910 census. But it is possbile that James and Mattie took in children from more than one sibling.

The SSDI lists Mabel McCormick, born 9 Jan 1901, died April 1984, last residence Mount Sterling, Montgomery Co., Kentucky.

The Kentucky death index lists Mabel E. McCormick, age 83, died 20 April 1984 in Montgomery Co., residence same.