Is the pain down her thigh nerve pain? It might be sciatica caused by inflammation of the periformis muscle located near the buttocks and hip. Could also be from the hips or the lower back. If it's the periformis muscle, it won't show on the MRI or an X-ray. For many people the sciatic nerve goes over that small muscle, and so when the muscle gets inflamed it hits the sciatic nerve and travels down the leg. I've had it, it's painful. I got it from intense bike riding. Can't tell you this is what it is, and with diabetics, there is so much neuropathy possible, but it's something to consider if they don't find anything else. Does she exercise at all? I ask because movement can help prevent some things, and it can cause others depending on the type of exercise.