This topic sparked my interest so I googled up on it. Basically (really basic that is) the MRC diet is a low carb diet and they want us to go into ketosis to help with fat loss. Right now, there's a lot of research on ketones and being bi-polar, like being on a low carb diet may actually help control mood swings. Also, the hormone seritonin (a mood elevator) is produced after eating carbs. Since this is a low-carb diet, our seritonin levels could possibly be lower causing mood swings. So in all reality, MRC is protecting themselves by not allowing people that are bi-polar on their program because the diet itself causing mood swings and they don't want to be responsible for anything that could happen with the added mental condition.
The best thing to do is to talk to her doctor about this and have him/her help with finding a weight loss program that would be best. Show him/her the menu and discuss it. Most likely, MRC is going to stick to their decision, but since you and your husband are on it you both can help keep her on track if you decide this diet will work for her too. And we're here for you too.
Something else I thought was interesting, I found another forum on low-carb diets and they have a group there of people who are bi-polar and trying to lose weight. It may be usefull. http://www.lowcarbfriends.com/bbs/ge...wn-thread.html