Rice cakes are not on the original protocol and I don’t have any familiarity with ladies using this, but some people who are gluten free replace the grissini/melba with a similiar gluten-free starch – it’s possible that a rice cake equal in calories might be alright – for instance here you can see 1 grissini breadstick from original protocol is 20 calories:
If you eat a little over half a rice cake – .6 to be exact, that is about equal to the grissini calories. A whole rice cake has 35 calories.So this may be a suitable substitute here.
You can go over the foods allowed on the diet and modifications to the food list some have made here: Phase 2 Basics