It seems like (other than athlete's foot, which is easy to spot, so I'm guessing it's not that) most cases of burning feet are the result of nerve damage, and for that, you and the doctor need to figure out what is causing it and stop the cause. You're pursuing that angle already.
The only thing that I've seen that could fall into the realm of home treatment is that, if your girlfriend has a particular vitamin deficiency (folate, B-12, and/or vitamin C). Those, you can administer at home as it won't hurt to take some more vitamins even if that isn't the cause. I wouldn't take more per day than 800 micrograms of folate, more than 4 micrograms of B-12, or more than 1500 milligrams of vitamin C; and even those amounts, beyond about a week, I'd cut back to half those values on an ongoing basis (to get back to 100% RDA instead of more).