I was about to say everything Sherry just shared. So more than anything, I’m simply affirming her suggestions to you.
Weight bearing and resistance activities stimulate the production of new bone cells. Some research indicates that this comes from the cells being jostled during movement. As such, some doctors prescribe low intensity vibration therapy: http://www.askdoctork.com/can-vibration-therapy-prevent-osteoporosis-201…. This isn’t universally recognized as being helpful, but it’s something to consider researching more (and discussing with your client’s doctors). If you have access to a high quality vibration plate machine, it could be a useful tool.
I hope you are well,