There is a Grace on the 1910 census that is not on the 1900 census. They may be the same person. They are about the same age.
I think Mary and Grace may be twins or are the same person.
1900 Census for Goshen Hill in Union South Carolina
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Mary is 26 degrees from Herbert Adair, 22 degrees from Richard Adams, 21 degrees from Mel Blanc, 23 degrees from Dick Bruna, 19 degrees from Bunny DeBarge, 34 degrees from Peter Dinklage, 19 degrees from Sam Edwards, 18 degrees from Ginnifer Goodwin, 20 degrees from Marty Krofft, 18 degrees from Junius Matthews, 17 degrees from Rachel Mellon and 21 degrees from Harold Warstler on our single family tree. Login to find your connection.