How can further deterioration of kidney of my mom can be avoided via foods and medical treatments? creatinine-251micromol/l,potassium-4.8 age-65

I assume your mom: has had other tests to confirm that she does indeed have kidney problems. The best way to prevent further deterioration is proper treatment of any disorder that might contribute to or worsen kidney function. Drugs that might be toxic to kidneys must be avoided. As far as food, limiting salt intake and staying well hydrated may help. No other food advice needed as long as potassium is normal.