You may have already checked this, but did you take a really good look at the vent area of your EE hen? I believe she probably has other issues going on, but it is warming up now which means mites. These can really set a chicken's immune system back, and I have had situations where only one chicken of the whole flock had problems with them. It's worth checking if you haven't already.
I'm not much help on the main diagnosis, but adding a probiotic/vitamin to the water certainly wouldn't hurt.
Good luck, and please keep us posted.
I'm not much help on the main diagnosis, but adding a probiotic/vitamin to the water certainly wouldn't hurt.
Good luck, and please keep us posted.