Does she really eat every minute of every day? (And my children are working in an office already?) There are several ways to approach this, although none of them is perfect, and none of them is guaranteed not to get Twix crumbs spat into your eye.
You can start by wearing noise-canceling headphones. You can have a private, respectful conversation with her without any passive-aggressive hints and simply say, “I like sharing space with you, but I have to confess I’m sometimes distracted by the snacking.” You can approach your boss for guidance (notice I didn’t say to complain, but to troubleshoot).
Whatever solution you choose, go heavy on respect, don’t make it personal (make it about the presence of food, not the grossness of her eating) and focus on the big picture. After all, there are five different senses that co-workers can offend: You might be lucky this is just one or two.
Of course you want to “win,” because you feel that your view is the best one. No crime in that! But this needs to move from a competition to a collaboration.
Get rid of the black-and-white, this-way-or-that-way thinking. He can try a school without it having to be forever.
Quantitative markers can be set up that take all of your views into account. Schedule meetings with relevant experts: principals, specialists, physicians and teachers. Talk to current parents. And don’t forget to keep a dialog open with your son and really listen to his thoughts about it.