If this helps, Denison is in Grayson Co, TX. Sherman is the county seat and they have a nice little genealogy collection. You might contact them, see if Gertrude donated a copy to them. I do not see the book listed on WorldCat, but not all libraries are represented on that catalog. Local genealogical society uses the same street address.
Sherman Public Library, Local Hist & Gen Dept PO Box 1106 421 North Travis Sherman, TX 75090-0190 (214) 892 7240
Maybe they will know something about Gertrude and her book.