Definitley share with the school and your daughters teachers that you would like her to stick to a healthy diet. You don't have to mention that you would like her to specifically thin out if you are not comfortable with that, but letting them know can help if she is getting daytime snack that you are unaware of. A lot of school provide snacks even though they do not provide lunches, and having an extra eye in the classroom to make sure she is not gettin anything other than what you provide is a good idea. Also, kids in classes this age tend to have a lot of birthday parties, holiday celebrations, and those events almost always include cookies, cake, candy etc. by providing your daughter's teacher with a healthy alternative, something perhaps that your daughter doesn't usually have, but is less high in fat, sugar, and calories than cake, would be great. Or just asking the teacher to limit your daughter's portion might work, although at that age kids do notice every little discrepency in portion size compared to their peers. Since it really is about her health, it wouldn't be totally unethical to stretch the truth a little with her peanut allergy and use that as an excuse for not wanting her to eat anything that has been prepared by you.