I believe everyone has some level of fungus or candida in their bodies. It's only when the ratio of bad to good bacteria gets out of whack that it starts causing issues. I think the vast majority of overgrowth issues are precipitated by antibiotic courses, so I would definitely ask her to check her medical history for the cause. There is also the possibility that it is environmental as certain household molds could be wrecking havoc.
As far as treatment options - Garlic appears to have more
effective anti-candida activity than nystatin and is a very potent antibacterial in general. Other things like oregano oil and essential oils are also strong in wiping out some pathogens. Sugar and stress elimination are also important for normalizing things.
The only kind of medical practice that would recognize it is an integrative one, but they charge quite a bit. I think she could look up a lot of the information online and try it out herself.