I just did a quick google search and found Maple Sugar Urine Disease which is a genetic disease that prevents making enzymes that breakdown amino acids. There are several forms of this syndrome that can appear at any age. Some of the symptoms might be what your mother is experiencing. Mayo Clinic is definitely a place for testing her to clarify what her true diagnosis is which may or may not be involved with hearing loss. It can be difficult to tease out the strands of a rare condition like this. Proper diagnosis can lead to treatment. Good luck in your search for an answer and its wonderful you are helping your mother to feel better.