Re: School lunches and an unhappy kid!
Awww, I get where you are coming from. If that is a passion and you want your daughter to continue eating the way that is best for your family just continue to stick to your guns and keep letting her know why you do what you do.
I used to be very very picky about what my son ate and he 'got' it. I still can be that way but not at all like I use too. I pack his lunch everyday [he is SPD/ASD so he's picky anyway and won't eat a lot of what is served at school].
As far as snacks and snack time, I wouldn't let it upset me what other parents do. Just like you have the right to send healthier snacks, they have the right to send what they want. I honestly let my son have those snacks and enjoy himself. He is in kindergarten as well. However he's been in a special needs school for 3 years prior to that. I've become a lot less stringent on things.
Sometimes the grass is greener on the other side!