I Googled various combinations of "egg shell calcium", "egg shell calcium bone density", "egg shell supplement", etc. on Google scholar. There are many studies out there supporting what you posted, if the egg shell calcium supplementation includes vitamin D3.

LizaJane's concern is that she may not have living osteoblasts and osteoclasts to utilize supplemental calcium. I'd expect that if that were the case she would have been experiencing multiple stress fractures in the highly stressed bones of the feet, hips, and jaw over the past few years. That hasn't been the case, which to me is cause for optimism. It will be clearer with further testing.

Not to beat a dead horse, but long term use of any drug should be only in case of dire need and approached with caution. Even with well established drugs like those to lower blood pressure, I ask my physician to prescribe drugs with different modes of action every year at my annual checkup. I recently switched from Lisinopril to Cozaar. Both seem to work equally well to control hypertension, but my hair is still migrating from the top of my head to the insides of my ears, nostrils, and my back. Life is so unfair.