Then I forgot all about it.
Didn't even notice when revising. Only after I had finished the scene did I think, hmm, when she fumbles for the bridge in the dark, the bridge, and the earth, ought to be wet.
Went back for another pass, and realized that it needed to stop raining -- or keep raining -- and either way, there would be a lot of mud in her way through that encounter.
sigh. Will retackle it once the idea sinks in.