Calcium by iteslf is not going to help. Calcium citrate is good for most.
Vitamin D Council > Health conditions > Musculoskeletal > Osteoporosis
Vitamin D sufficiency is key. She should get tested right away.
Also sufficient Magnesium (400-600 mg/day--most need to supplement), not too much calcium (500 mg/day is fine from all sources) and sufficient K, zinc & boron via diet.