Hi.. Thanks for the query.. It looks like her yeast infection is progressing to her mouth also and it is leading to eruption of mouth ulcers due to inflammation and also burning sensation is due to infection.. She should be evaluated by an Oral Physician and scraping should be taken from her mouth and should be microscopically examined.. In case if thrush is progressive then she should be advised oral antifungal medications like Fluconazole, Itraconazole along with sucking Clotrimazole lozenges and doing Nystatin mouthwash gargles.. For reducing burning you can gargle with numbing mouthwash containing Lignocaine.. Take plenty of probiotics like Yogurt.. Take Vitamin B complex supplements.. Hope this helps.. Regards..