Grandma is 88 years old. stick thin. at night she has pain in her legs, due to which she can't sleep. reason? she takes calcium, vit d, folic acid.

Not clear: Take her to a good physician. She needs a good workup. There have good studies recently published which demonstrated that the taking of calcium and Vitamin D together did not improve bone health. That's why you have to do double-blind studies in medicine! Things that at first thought you might think "Sure, that will work." frequently do not!

Many possibilities: If the pain is cramping it might be corrected by nutrients, though might be caused by arthritis, degenerative disc disease in her low back etc. so she should see a Dr. for evaluation. If cramping try Magnesium as glycinate or taurate about 300 mg/day- deficiency is common; it's mostly in leafy greens,nuts & seeds. Vitamin E and B12 deficiency could cause; low B12 common at her age, may need shots.