A few things:
First, the PP is correct that many girls around this age become chubby. They do vthis before they shoot up (and get curves) as part of puberty. There may be an overreaction going on--please do not make the girl feel badly about her body. Perhaps, out of the girl's hearing, mom should ask the pediatrician on their next visit if this is normal or really a problem.
That said, eating healthy (not with the intention to loose weight) is always a good idea.
I notice yo usaid she takes baekd chips. While better than regular chips a whole pacakge of these is still a lot of empty calories. I would not be sending things like that every day, or if she really wants the crunch and salt just send 4-5 chips in baggie. As a general rule of thumb avoiding anything (other than yogurt) that comes in individual packages is a good place to start (this would include most granola bars which have a lot of calories and sugar and often fat without a whole lot of nutrition). Also watch what goes in as a drink. I would suggest only water (no juice boxes, etc.).
I think it helps a lot to think beyond just a sandwhich as an entree (as others have pointed out). Also think beyond jsut lunch meet for fillers for wraps. Neither of my children will eat school lunches so I pack 2 lunches a day, here are some typical things:
Entrees
Wraps made with:
*lunchmeat and/or cheese and veggies
*light cream cheese, diced fruit and cinnamon
*peanutbutter, diced apples or bananas (and sometimes a few minicholoate chips with the bananas), sprinkled with homemade granola
*hummus and veggies
Pita pockets filled with:
*cheese and veggies
*tuna or chicken salad (make with plain yogurt instead of mayo)
*salad (pack a light dressing in a container to add at lunch time
Fruit and cheese kabobs
salad with cold chicken breast strips
boiled egg with whole grain crackers
cold pasta salad
bagel with cream cheese (light) or peanut butter
nutella or peanutbutter in a container with sliced fruit to dip in
container full of mixed nuts and cheerios
For sides I always include a piece of fruit. I often include yogurt, and usually some other grain (a small baggie of pretzles, dry cereal, muffin, etc.)
I do like to include a small dessert (I do not like things to be too off limits). By small I mean ONE small tootsie roll, one andes mint, one mini peanutbutter cup, etc.