My daughter suffers from that problem and I am a doctor in nutrition so I usually cook without gluten and I worry about this issue. Many of my clips are gluten-free cookies. I use pure corn flour in the same recipes as with other cereals. There are different brands of flour like proceli or search ( Europe). No problem about that, but not every brand of meringue powder is gluten-free. In fact, many of the brands have almidón . . . so maybe whites and sugar would be a better option or see if your specific meringue powder is gluten-free ( for example, Wilton contains almidón so I can't use for my daughter) - the same with the colorants, but Sugarflair is gluten-free and AmeriColor is good as well.
[EDITOR'S NOTE: FYI, almidón = starch in Spanish; I'm presuming starch from wheat based on the above comments.]