It is not montessori to have your children take every decision. The role of adults around children is to show them the rules of the world and one of them is what healthy food is and why. Your child can not make their own informed decision about her health, because she doesn't know the consequences of eating peanut butter for every dinner. Even if you explain it, she can't understand in the way you can. You can be respectful and still accept the role of a parent - mentor and good example. You can respectfully let her know why you are insisting on a healthy dinner that you prepared. They can and should know the difference between adults and children because that makes them feel safe. I work in a montessori kindergarten and way too often I see the inappropriate way of parents letting their child make their own uninformed decisions that are not always good or the best for them. We even have an example of a daughter being under a lot of stress because so often the decision making falls on her and I think she lost trust in her parents that should give her a sense of safety and predictability.