Talk to Internal Medicine on Mouth Issue

My Mother is 55 years old. She is diabetic. Few months back she developed a condition where she used to have blisters, lesions in mouth. Which were painful they used to come and go every now and then. She tried controlling her sugar levels which were too high like 350+. After successfully controlling her sugar she got relieved for some time. Later on her sugar fluctuated and again this condition came back this time even more strongly. We consulted Dentist. He gave medication like Injection decadron 4mg/1ml (for oral ) Revomet antibacterial gel During 7 days course she felt relieved everything was gone. But on the 9th day it came back worst. She developed some fungal inside her mouth. (tongue picture is after using decadron and revomet)

Then doctor gave Deckarin gel Velolog gel Nilstat drops It's been 6 days now she is not healing. Extremely in pain. Not eating anything. Please kindly recommend anything for her