Welcome To BYCThank you for writing this up, I'm very sorry for your loss, and very grateful that you have shared all this information.
I'm currently trying to rid my Chicken of Gapeworm. She seems healthy and fine, I think she has been infected for about 5 or 6 weeks now. I treated her with the Avitrol Plus Bird wormer 4 weeks ago, then again 2 weeks ago, and an extra dose a week ago. I think after reading your experiences I will wait and see if the worms leave or not, before moving on to the Flubenol. She seems 100% fine, except for the cough / gurgle noise. She hasn't been gaping for about 2 weeks now, but started a few days ago with the cough / gurgle noise through the night! Fingers crossed.
Sorry you're having troubles.
The OP (Original Poster) has only made 1 post in 2022 and has never returned, so very unlikely they will reply to you.
Where are you located in the world?
My understanding is that Avitrol Plus is given once, then repeated in 14 days. The dewormer should have taken care of Gapeworms if this was her issue.
Generally, a chicken that has Gapeworms gasps constantly, is in distress and is not eating/drinking.
You report she's healthy and fine, but started a gurgle/cough noise a few days ago.
Check her crop - make sure it's emptying overnight. Gurgling can often be heard when a hen has a crop issue. https://www.backyardchickens.com/ar...w-to-know-which-one-youre-dealing-with.73607/
Is she laying eggs? Any bloat or fluid in the abdomen? Gurgling can often be heard when a hen has fluid in the abdomen.