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It sounds like you are in a tight situation. Unfortunately, the scans are the next step. Infection vs. Cancer seems like it would be easy to determine...but in certain locations, sometime we don't know. The areas are hard to penetrate with medications...the assumption would be infection due to her age...but we never know.
You are probably seeing wonderful veterinarians who want this to be diagnosed almost as much as you, but it may not happen...the scans would be next.
The failure to really respond doesn't mean it is not fungal.