Roux-en-Y gastric bypass creates a malabsorbtion syndrome as well as mechanical inhibition to ingest large volumes of food. The malabsorbtion can make them susceptible to vitamin and nutrient deficiencies. Iron, Vit B12, Vit D, etc. She should be taking supplements. I think the Zone method of nutrition is ideal for these people. I wouldn't tell her to skip the vitamin supplements. The Zone to me is just a very healthy way of eating. I don't know what kind of counseling she received from a nutritionist (this is usually part of any person undergoing these procedures), but I can't see any reason why they or her doctor would disapprove.
Congrats on helping her with Crossfit (my brother is a Crossfit trainer also) and she needs to continue the healthy fitness and nutritional way of life. These people can and do revert back to gaining weight over time. Hopefully she can change her lifestyle.
As far as calculating blocks, that just isn't my thing. I just know the general idea and adjust eating accordingly, but I don't have the personality to sweat over a block of this or that so I can't help you there.