Sounds strange, but if you deal with authorities - don't expect them to make much sense. They'll probably argue that once you add water to meringue powder / dried egg white, it will be just like egg whites again (totally ignoring that dehydrating kills all salmonella which might have been in there at the start...)
I keep my fingers crossed that you will get them to include meringue powder, but if the authorities in the States are anything like they are here in Germany, this might easily take a decade
So, how about trying a vegan icing instead? There are a lot of recipes for that and they seem to work just fine. This way you might get your business started even if there is no chance to work with meringue powder.