Why The Cramps On Feet Start From The Abdomen Area?

Hi I was massaging my mothers feet, and on both of them her index and middle toe cramp together yet the pain starts from the digestive system and from what I see the kidney area on both feet, what is this caused by? Is it a nerve impingement? She had just recently had foot surgery and had them fused. Could it be from walking too much? Should she rest? Soak in hot water? Help!! Thank you.