Telegraph code books were put out by many
different publishers, sometimes for the general
public and sometimes for use in specific
commercial interests such as cotton trading,
mining, railways, etc.
As for what the message actually says, well that's still a mystery. I sat in bed with my cold for hours pulling up old telegraph code books on Google books and then looking for some of the words that appear in my message: event, none, lining, etc. Occasionally I even found those words and the phrases they represent. But alas, none of the books I looked at had all of the words I needed.
It turns out there are thousands of telegraph code books. Apparently the owner of my dress knew that the person she was writing to had the same book for decoding purposes. If only the first word was some clue as to which book was needed! But no such luck. Only some telegraph code books are available online, and the one I need doesn't seem to be among them. I could go into D.C. and spend hours at the Library of Congress to see if they have the book I need, but the problem is I have this other obligation, commonly known as a 'job', and people actually expect me to make the time to show up there. And so, months later, I am still unable to follow up with the complete solution to my mystery. I'll keep an eye out for code books, and I'll keep checking them, but for the time being, I'm putting this investigation to rest.