Chris: There are 9 Levi Coffins in "Coffin Family" by Louis Coffin. However, I was able to find the one you're interested in because of his work with fugitive slaves and the underground railway, which is cited in the book.
Levi-6 Coffin, s/o Levi-5 Coffin & Prudence Williams of NC, m. Catharine White, d/o Stanton & Sarah White.
The children of Levi and Catharine:
Jessem. Meekey B. William Addison Thomas F. Henry W.m. Sadie E. Amick Anna U. Sarah Emeline
You think that Edna Davis was gdau of Levi Coffin. Since Davis was her maiden name she would have come from a female line...either Anna U. or Sarah Emeline must have married a Davis.
The problem is that very few female lines are shown in the book. I checked that section of the book but found nothing there for either of Levi's daughters.
Levi's line traces back to John-2 Coffin, s/o Tristram-1 Coffin and Dionis Stevens. John's wife was Deborah-2 Austin, d/o Joseph-1 Austin and Sarah-2 Starbuck. All were on Nantucket. John-2 later moved to Marhta's Vineyard where he is buried.