hello, since your mother is on dialysis, due to long standing swelling of leg , which can cause pain during flexing her toes. if her sensation are normal in that area then no need to worry, reducing swelling and some
vitamin supplements will bring her back strength, if she is
diabetes and there are no sensation on that toe then she need to undergo nerve conduction studies, dont worry she doesnt need mri brain and it is not serious condition. please visit an orthopedician to find the cause.