Not particularly relevant to the book but I'm blaming the neurospicy brain.

Glue has a very long history, with (from my knowledge) the oldest known glue having been made and used by Neanderthals. Although glue wouldn't gain popularity in Europe until the 15 to 17 hundreds. It could have been produced by either cooking animal skins or plants. Synthetic glue was invented around the 1920s and production of animalistic glue would start to decline. So no Elmers glue is not named after the first horse to be turned into glue and the glue you buy today is most likely a synthetic one.