I guess the title says it all. Antifungals have been tried but it always comes back.
Its hard. The foot environment is conducive to athelete's foot in this person for some reason, and unless that environment is changed, it will keep coming back.
There's a few things you can try:
Athelete's foot can be one of the symptoms of systemic candida overgrowth. So if the person has any other symptoms of yeast overgrowth (such vaginal yeast infections more than once a year, sores on the corner of the mouth, diarrhea for no reason now and then, etc) then an anti-candida diet would be a good idea for the whole body. You could do a google search on candida overgrowth for a complete list of symptoms and how to treat them.
If that's not it, then:
The feet probably sweat a bit more than the average foot. So... go barefoot as much as possible, change socks a few times a day, wear sandals instead of shoes, etc.
Some people soak their feet in Scope (a mouthwash) every night and swear that works. But that's still just killing the fungus every day, not really changing the environment.
The fungus that causes athelete's foot is present everywhere. Its not possible to avoid it.