Hi, I checked The Plumer Genealogy. It was written in 1917. I didn't find your wife's grandfather Herbert, but I did find the following: Rev. Charles Abraham Plumer, born in New Castle, N.H. feb 16, 1839. He was educated at Bucksport and Concord; and was a clergyman at Thomaston, Me. He married Mary Amanda Maddox May 5, 1861. Children:Willard Elmer b. Mar 23 1862; Osman Baker, b. Aug 1868; Charles Wesley b. Aug 21, 1872; and Herbert Hall, b. Oct 5, 1874.
Since the names Herbert and Charles are used in this family, I thought there might be some connection. You might look at the 1910 census for Rockingham Co., NH and see if you can find Herbert as a child and the names of his parents. If you can, let me know, and perhaps I can go further back for you. Good luck! Carolyn