If it's a hymn, it's an extremely rare one indeed. Even taking tiny snippets from your text, and then entering them into Google, finds no valid results. (Searching that way usually finds even the most obscure of hymns, even though there might be a few minor variations from the whole of the text that was started with).
Perhaps your mother jotted out a rough version on one piece of paper (complete with any crossings out or other amendments) and then copied the final result into the cash book that you've found? (When I'm writing poetry, I often start out with lots of bits of paper with rough notes on them before arriving at the final result, which I then write out or type into Word. I've just finished one poem that had bits of it written in various notepads over several years before I got it somewhere close to how I want it to be).