A.B.
I was a teacher in an elementary school and we always had Teaching Assistants at lunch with the kids, so there were always people available to open packages. I wouldn't worry about carrying a lunch tray. I've seen even the littlest kindergartners carry them. I would worry more about her not liking the lunch, so maybe send a lunch at first and see if she asks to buy lunch later. I would also suggest not sending peanut butter or peanut products, since a lot of schools now don't want you to send peanut butter because of allergies. The school I worked at had a separate table for the kids with peanut allergies but a lot of schools are banning them altogether. If you're concerned about opening packages, you could open them and tape them shut so they are easier to open. You could also work on teaching her now how to open them.