Non-Healing Wound in Throat & Hoarse Voice

My mother burned her throat on rice that was too hot in temperature. The first visit, the Dr. gave her a steroid and it didn't help. A week or so later on the second visit, she was given a gargle which didn't help. A couple weeks later she felt the pain was spreading from her throat to behind her nose and she saw the specialist and was given liquid hydo-codeine and an anti-fungal. He used a scope and saw a big burn and fungus on it. Over a month later she said the pain is worse than ever and her voice is getting a little hoarse. She seems to eat fine though.

When is it time for a biopsy? Is it possible a throat cancer can emerge from a burn wound and fungus?

I encouraged she take some zinc to help in healing but she isn't interested.