Your mother probably is suffering from a condition called Steroid induced Cushing's Syndrome
affect bone in three main ways;
1) Loss of bone mass,
2) Loss of bone protein and osteoporotic lesions,
3) increased urinary excretion of calcium and phosphorus leading to bone loss.
She should be evaluated by an endocrinologist
and undergo tests like overnight 1-mg Dexamethasone suppression test
or a 24-hour urine test for Cortisol.
She may need further medications depending on the test reports.
The patient should eat foods that are high in calcium and vitamin D and low in fat. To prevent the risk of fractures in patients taking steroids, prevention of falls is important. Drugs such as the Bisphosphonates
may be prescribed to prevent bone loss but you need to meet an orthopedician for this.