Diabetes' risks include foot amputations but does it cause this too?

Some people must have their foot amputated due to complications of diabetes. But does diabetes cause collapse of the foot bones?
An old friend of mine, a diabetic, had to have her foot rebuilt some time after knee replacements. She hasn’t been able to walk on it for months. Could this have been caused by diabetes? If it was from her being heavy on top, I assume this would have affected both feet.