Hi there There can be many reasons for her stooping forward posture. It can be because of a sprain in her back or occurance of denegerative changes, osteoporosis is common in women too, spinal stenosis can be one of the cause. She is bending forward more so it means she is feeling comfortable in that posture and might feel pain in back extension. And one of the cause of nails getting dark is deficiency of vitamin B12. I would recommend you to take your mother to a good orthopedic doctor as soon as possible.