This might sound strange, but I know Bag Balm works for chapped hands; people who are around farms swear by it! I get cracks on my fingertips in the winter; I use a product called NewSkin, which is a liquid bandage. It works quite well. I also keep them bandaged if I can (a pain since I'm always having to change them.)

If it were my feet I'd put the salve on, wrap them in gauze and only wear white cotton socks until they healed. People can be sensitive to the dyes in socks, or to the fibers themselves. Good luck to your friend and her sore feet.