It could have been part of her job:

> Rivers Cofield also notes that the dress – although beautiful and fancy to our modern eyes – was not exactly what someone would wear to a ball. It was more like the ‘business casual’ of the day, and to her that does indicate it might have been worn to work.

> Chan has also documented that a number of women worked as clerical staff at the Washington, D.C. offices for the Army Signal Service in the 1880s.

https://www.noaa.gov/heritage/stories/cryptogram-in-silk-dre...

Maybe she didn't know it was a weather report encoded in telegraph jargon and instead thought it was some kind of crypto puzzle that she kept handy to work on in idle moments.