You definitely need some lamps, heat and UVB, but that information should be readily available, and others on the site would know the specifics better than myself. You can and should give supplements more often than once week. Again, I'm not an expert but that info should be easy to find as well.
I mainly wanted to address the trouble pooing. You can help her by giving daily soaks in warm (not hot) water. It should help her poo more comfortably. If she's still having issues, gently massage her lower abdomen to get things moving. In the short term, that is one of the best things you can do for her.
In the long term, you will have to take steps to remedy and hopefully reverse the effects of MBD. A vet would be able to prescribe liquid calcium, otherwise proper heating, lighting, and supplements are essential long term.