My sister has (probable) Meniere's, don't know if she has a definite diagnosis but has had vertigo/hearing loss for more than a decade. She controls it by avoiding stress and eschewing all dairy. I have celiac (14 years) and control it with diet, but she won't get tested so is just gluten light. Consider keeping a food log in case some food(s) worsen symptoms. Stress is a big trigger, especially with you being a caretaker. Does Australia have care for caretakers? Will your mother wear headphones for the radio (more expensive ones can compensate for hearing loss)? For you, Bose or other good quality noise-cancelling headphones are helpful at blocking the squawks and don't irritate like earplugs. Regular foam earplugs are not bad, but silicone and high-density foam are better at dampening decibels (I also have low noise tolerance). If you haven't tried meditation, it can be useful for controlling stress response and insomnia. Good that you are training and have a healthy diet and hydrate. One hypothesis for Meniere's is that the inner ear fluid is no longer a closed system, that it is more sensitive to dehyration/salt levels than someone without the disease. So it is good to drink an electrolyte with salts when intensely training. We do spend time and emotions nibbling off the edges of our diseases. Great that you are looking for answers. ResearchGate has medical papers on Meniere's (boring so also good for insomnia) .
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6513907/