We went to a free summer lunch program in the park while my husband was out of work, and I was excited to see what they packed in their cold lunches. I dodged the bullet this year and my son doesn't need a lunch in kindergarten. But I still like having ideas!
They usually had one item from each category below:
"Main dish":
Tortilla wraps--a slice of American cheese (not Kraft singles, which state they are "cheese food." Look for Deluxe brand or buy at the big warehouse stores) and two thick slices of ham or turkey lunch meat. In a small container they provided shredded lettuce, tomato slice, and pickle slices to add (but I don't know why you couldn't put them on and have it ready to go)
Bagel with a small container of cream cheese. My kids couldn't eat very much of the whole-wheat bagels, though. They're kinda dry and heavy.
PB&J. You could also try peanut butter and banana (sliced bananas instead of jelly)
Fruit:
Small containers of applesauce, diced pears, fruit cocktail, sliced strawberries with grapes, watermelon, etc.
Whole apple (I prefer slices because my kids seem to eat more of them. They can eat an entire apple if it's sliced, but can't finish a whole one)
Veggies:
They always included a baggie with two broccoli florets, two cauliflower florets, and two baby carrots, with a small container of Ranch to make sure it didn't all end up in the garbage can :) My kids and I don't like raw broccoli or cauliflower, so they only ate the carrots.
Side:
Bag of Sunchips. Always Sunchips! They really are a lot healthier than any other kind.
Oatmeal/raisin cookie
Jello (or add fruit like crushed pineapple and make it your fruit)
Yogurt
We also like a sliced plain or egg bagel with a slice or two of real American cheese or cheddar cheese in the middle (add lunch meat if she likes that)
My kids love raisins (easy to buy in tiny boxes) and Craisins, dried apricots and banana chips. Those are easy to have on hand when you don't have fresh fruit.
If you put half the peanut butter on one slice of bread and half on the other, with the jelly in the middle, PB&J's are fine over night. They only get gross if the jelly soaks into the bread.
My kids also like PB&J "roll ups," on a tortilla and rolled up. It's kinda fun that way. You could try refried beans, some shredded cheese and a little salsa in a roll up, too.
My kids also love cheese 'n crackers. Again, the real American cheese or cheddar, cut into squares, with Ritz or saltines. One son hates meat, so he eats it like that. My other son likes squares of lunch meat to add. They like to build their own stacks, or eat them separately.
My SIL always has hummus on hand. I'd never had it before, but I bet you could do some roll ups with that and it could be tasty.
We avoid fruit snacks, because despite the name, they're just fruit-flavored candy. I also don't buy the individual fruit cups or applesauce cups because they're so expensive! We have small plastic containers and divvy up a can of fruit or jar of applesauce into them. You can also make a bunch of little cups of Jello in them. My kids would LOVE to have a small container of just mandarin oranges or chunk pineapple. And you can have a bunch all divvied up and waiting in the fridge to grab quickly.
You'll have to adjust quantities to fit her appetite, too. The lunch program was for kids ages 1-18, so it was sometimes too much food for my preschoolers (as ravenous as they usually are!)
Good luck!