I imagine they would accomodate the millet bread as a special request once you are there if you do not pre-order. I do have a serious allergy to wheat and I've had the millet bread at BOG. It's really not all that good compared to regular bread; although, I am very happy to have a wheat free option so that I can eat safely. I'd happily trade the millet bread for gluten-full pastries any day, but if your daughter is wanting to try millet bread, Udi's gluten free brand makes millet bread you can get at most grocery stores and Target.
It's not my intention to make anyone feel bad about their food preferences, but as someone with a horrible food allergy, it is extremely hard when people indicate an allergy and then eat something at that restaurant they claim to be allergic to. The result is that food service professionals no longer take our allergies seriously and think we are being difficult or exaggerating. I've had this happen in multiple restaurants and I've gotten very sick--as in missed two weeks of work-- as a result. It's also embarrassing to have to explain to a server that "it's a real allergy that must be taken very seriously and no, they cannot just pick a crouton off and give me the same salad" at a business meal, for example. Just in case anyone can learn from reading this thread, please know that if you have a preference, you should just order accordingly--as a preference, not an allergy, as it really does impact people more than you might guess. I imagine that's why there were some terse replies--it's a hard thing to live with when there's no choice. OP, I appreciate that you plan to do that and I hope your daughter is able to order everything she wants--Disney is usually great about those kinds of things!