If she happens to be eating too many treats and getting full on them instead of the crumbled feed... It's also possible that she's not getting enough protein in her feathers are breaking because of it.
I'll find a few pictures for you to show him of what happens to hens that eat treats daily. Maybe the pictures will help him to see what it causes.
Your bird that's breathing funny...may already be suffering.
Antibiotics from a vet are one option to try. If a vet is not an option let me know...
Don't worry about Marek's disease coming in from wild birds. You are more likely to bring the dease home if you buy chickens from someone else.
Tapeworms and gurgling aren't a sign of Marek's.
Scratch and mealworms daily aren't good either. That's a lot of fat and takes away from the balanced diet of the crumbled feed.
Did she just start the gurgling after you gave her the equimax?
The stress can cause them to molt. Having a lot of tapeworms like isn't good.
Post in thread 'The Truth About the "Pea Sized Blob" of Horse Paste De-Wormer' https://www.backyardchickens.com/threads/the-truth-about-the-pea-sized-blob-of-horse-paste-de-wormer.1141545/post-17748695
The gurgling...