There are hormonal tests (FSH and LH) to determine the functioning of ovaries. It is said that, all women will eventually have menopause, and are at risk for osteoporosis. The most prudent thing to do is to take enough calcium (1200-1500 mg per day), and do some sort of aerobic exercises every day (walking is the best and safest).
There is also the option of bone density testing. If her bone density is low, she will need to be on some bone strengthening agent in addition to the calcium. If there is a family history of osteoporosis, then she is at a higher risk of developing it too.