Thanks again. Working on the assumption that she might have been known (or at least recorded) with a different surname, I've done some more aearching but still no sign of a marriage record. So my notes re John read "He may or may not have married Louisa Maria Hadley at some time not yet found but probably around 1895."
Unless there are some marriage records squirrelled away that have not yet been transcribed to a website, it looks as if they never married. One of those brick walls, I'm afraid, but again many thanks for the interest.