As a doctor, I just gotta point out that ménières is pretty well researched (though not completely mechanically figured out) but not in the "psychosomatic" corner like fibromyalgia, so please don't spout anti-vacc tier conspiracy retardedness about medicine when you have a basic internet forum level of knowledge. Just stick to discussing anime girls.
Edit: Also, fun fact, the risk of it going bilateral is about 25%, but it usually debuts around the age of 40, so assuming Kanata is not that old I'd say her risk of going fully deaf at some point is relatively high.
Edit2: To elaborate a bit on why your "suspicion" is wrong, ménières does not just cause hearing problems, in fact it has a pretty unmistaken clinical manifestation of recurring crippling attacks of vertigo and nausea that can last for hours or even days (among some other things). The diagnostic process is also one of eliminating differential diagnoses, not just making a guess and going for it. The hearing damage comes from nerve damage after every attack, which is why it is permanent.