I agree with Lightbringer's excellent suggestions.
The only thing I would suggest you may want to do differently if you would rather use totally raw garlic is to use a Garlic Press to press the garlic into a mash, and then rub the pressed garlic into the feet with or without being mixed with any oil, and then soak the rubbed feet. At least that way you know enough of the garlic got where it is supposed to go.
If perchance the raw garlic should burn his feet (I don't know if it will or not, but I doubt that it would), *then* the burn can be stopped by following up with a plain oil rub, possibly in addition to a cool soak, but I do not think that will be necessary at all.
It sounds like the lady you mentioned had heard of using a 'maceration' of garlic into oil, which can be accomplished by using mild stovetop heat or, as some others do it, leaving the garlic-in-oil out in the Sun for a couple of weeks. A perfectly valid and traditional way to use the herb.