How To Gain Fat In The Feet?

Hello... My Mommy has severe pain in her feet... we checked with an ortho doctor and he explained to me that she does not have anymore fat in her feet because of which she gets that pain when standing or walking. He advised her to wear soft slippers even when at home. He also gave pain killers, but thats only temporary relief. Could you please advise how this can be cured completely, and how can the fat in the feet be developed again?