I'm glad she is doing better. I have never heard of doing any antibiotics for 45 days. What exactly is the point? To prevent reinfection? They only time I have ever heard of long term antibiotic use is with recurrent UTI's. We are having that issue with one of my dogs and we still haven't...
Here is a more scientific page and it says it takes about a week for incubation and symptoms in a controlled infection.
http://wildpro.twycrosszoo.org/s/00dis/Parasitic/Gapeworm_Infection.htm
I found this on gape worm but have no actual experience with it. I don't think most people actually routinely worm their ducks. I also know ACV can help with worms, I just don't now what kind.
http://poultrykeeper.com/duck-keeping/worming-ducks
Did the antibiotics help at all? ACV is really safe and good for you so I would do that for a while. I don't really know what else it could be. Is she back to acting normal? Maybe some vitamins too since it won't hurt her at all and can help her kick whatever this is.
Both my pekins had creases in their chest. It is normal and just part of their make up. Have you tried Apple cider vinegar (with the mother). I found it help when one of mine started to cough. I had one that would almost hiccup and it never did go away but never caused any harm. He is...