I guess I feel like there must be more going on though? It's not clear why a weather message would have been hidden away like that. What I read about it suggested that the weather code system was more for telegraph message "compression" reasons than secrecy, although I don't know anything about it so could be missing something.
My guess is that the message must have had some other meaning in some way, even if personal, or that there's something about putting paper in the pocket for tailoring reasons?
Maybe she just needed a place to put the message and forgot about it.
The obvious theory would point out that female clothing isn't supposed to have pockets at all. This means that anything carried in any pocket is likely to be carried in a "hidden pocket" - that's the only kind of pocket.
My guess is that the message must have had some other meaning in some way, even if personal, or that there's something about putting paper in the pocket for tailoring reasons?
Maybe she just needed a place to put the message and forgot about it.