My mom is 55. she is experiencing an expansion/shifting of bone just above the heel in the backwards direction + frequent momentary intensive pains?

Sounds like.....: It sounds like your mom may be getting posterior tibial tendon dysfunction . This is not uncommon and will cause a the talus ( the bone above the heel) to rotate and drop. It will also be quite painful at times. My advice is to have it examined by a specialist. In the meantime have her try and stay off of it as much as possible, don't go barefoot and wrap i an ace bandage around it for support.

See a podiatrist: I agree that your mom should get evaluated by a specialist. While she may be experiencing a tendon dysfunction, there are many reasons why she could be having pain above the heel. Another common diagnosis is achilles tendonopathy, haglunds deformity, retrocalcaneal bursitis or pump bump. Something as simple as an open back shoe and heel lifts may help alleviate some pain. Again, see a physician.