Hen with rapid, labored breathing

I have a 2 1/2 year old Comet hen, Dixie, that has recently exhibited labored breathing that is also faster than normal and slight wheezing; she is able to breath without opening her mouth though.

She also has had an accumulation of dried on feces in her vent area for some time. After checking here about that condition, I gave the hens a few days of "Strike" worming meds in their feed and also have been adding probiotics to their water for just over a week. Today, the weather is warm here in NH so I gave her a bath in water with Epsom salts, removed the feces and used a blow-dryer to dry her feathers.

This hen's labored breathing seems to have developed over the past week. She is eating and drinking fine, her weight is good, but she is somewhat subdued in her behavior. When I let the hens out of their coop, she always lags behind, although when she sees me with a bag of mealworms she can move along pretty fast! She stopped laying quite a while ago, so I don't think she is egg-bound.

Is it possible that she has had a bad reaction to the wormer? Has anyone else used "Strike" pelleted wormer? What else should I look for? Any help would be appreciated.