My mother is a healthy, active ninetyseven y/o. She has never had a yeast inf. But c/o vaginal burning. What could be wrong?

Few reasons... Suspect 1. Dry atrophic vaginal wall. 2. Was on an ab, changing normal bacteria-yeast ratio, causing yeast overgrowth-infection (easily treated). 3. Could be a cystitis (infection of bladder) or uti--extremely common in elderly--can be spontaneous, or some stool organisms get into urethra setting off infection. This, in elderly, may not have any sx or different than typical sx, but lead to sepsis.