Who is the author that made Mary had a little lamb?

According to other sources on this site, "Mary Had a Little Lamb" was written by Sarah Josepha Hale in 1830. This is when the song was first published; but according to "The Story of Mary's Little Lamb," published in 1928 by Mr. and Mrs. Henry Ford (yes, that Henry Ford), in 1817 one Mary Sawyer brought her pet lamb to the Redstone School in Sterling, Massachusetts. Visiting the school that day was a ministry student named John Roulstone, Jr. According to Mary Sawyer's own testimony (in the Fords' book and in Sawyer family records), Roulstone revisited the school a couple of days later and gave her a poem that he had written in commemoration of the obviously historic event.

If we only credit Hale as the author of the song, then Mary has no surname. But if Sawyer's account is true (and Roulstone wrote the poem, with Hale later adding some verses and the melody), then Mary's surname was Sawyer.