What causes burning feet?

I am trying to help a friend. She says that the soles of her feet constantly feel like they are burning. She says that if she stands a long time during the day and then puts her feet up it feels like they just go numb. She says it has been like this for years and she is worried that it is MS because MS has been present in her family. I read on this site that MS is not heriditary though.

Would you please respond with ideas of what might be causing this so I could try to help her?