I am an audiologist, and I want to point out that there are two main "types" of hearing loss. If a change in diet resulted in improved hearing, the cause of the hearing was likely a "conductive" hearing loss, due to the mechanics like the eardrum or bones of the ear not funtioning properly (often due to allergies, sinus problems, fluid buildup, infection). Often, Conductive hearing loss is temporary, or may be resolved through surgery, medication, diet change, lifestyle change (eg. quit smoking)
Another type of hearing loss is "sensorineural", which is typically a permanant hearing loss, that diet will not change. This is a deterioration or damage to the hearing nerve which cannot be reversed. A common "nerve" type hearing loss is the "noise notch" as well as general age related hearing loss "presbycusis". Sometimes however, this can fluctuate with Meniere's disease, but it isn't due to diet.
The "nerve" type loss is the more common of the two, and again, cannot be reversed. The "conductive" type is less common, and had potential for remedy.
Her hearing loss was likely conductive overall, which is why most of it had improved, however her "noise notch" (nerve related) did not improve.
I just don't want people to have false hope that a diet change will cure their hearing loss, unfortunately it's not that simple.