In that case next time you water, water a little extra heavy and get 20% run off out the bottom of the pot. The goal would be a gentle flush of that one plant to get out some of that manure. Be sure to keep the plant out of the run off water, you don't want them to such that back up.
Trust your soil even though you know nothing more than starting pH the plant will go slightly yellow when she needs feed. I'd stick with cannabis specific nutes until you have a couple grows.
She should recover well enough and since the others aren't affected I wouldn't worry.
Is the affected plant a totally different strain?