There are many possible causes of bone lysis from cancer to infection. You've probably heard of osteoporosis. This is a common metabolic disease that can cause bone loss. This type of bone loss is usually more diffuse.

Joint replacement has become a popular treatment for arthritis. Bone loss around the implant is called peri-implant lysis. This can occur when there is a delay in bone healing for any reason.

It's not clear from your question what could be causing your aunt's bone loss. A specific diagnosis must be made in order to treat the underlying cause, not just the symptoms. If possible have your aunt contact her doctor and get some more information about her condition.