My daughter is 17 and a Senior. At her school, it is only Juniors and Seniors and you can leave campus for lunch. Sometimes, she does this but not often.... most especially, she will not drive if she goes off campus to lunch because she leaves at 7:15 am to get to school to get her parking spot and her first class is at 9!
Most of the time, she has a water bottle/Vitamin water and assorted fruit snacks, protein bars, etc. She does eat a good breakfast and she does come home starving. She is in Varsity cheer so she is in practice from 2:30-4:30 daily. Her school day is appx 7:15-5 unless there is a game (volleyball/basketball, etc) and those keep her out until about 10pm unless it is football and those are later but on Friday nights. She gets home about 5 and I have something ready for her that is hot or ready to be heated when she gets home to unwind.
Some favorites are homemade marinara and pasta, caprese salad, sausage balls, burger, grilled cheese, Stouffers lasagna, salmon, veggie soup, minestrone soup, chili, beef stew... all homemade, etc.
As for the junk food, we just don't eat it often at all. Even as a toddler, you could offer her an apple or candy and she'd pick the apple. We don't do desserts at meals either. Very rarely will we induldge in a dessert.
I couldn't tell you what is in the Sr high school cafeteria because her spending acocunt has not budged for 2 yrs so I know she is not buying anything there. They do have "stay in's" about once a month where companies bring food in and it is a huge hit... BBQ, Chick Filet, Deli places, etc.
I don't monitor her eating habits because she is old enough to know the cause and effect of eating junk which is lower energy, weight,gain, etc. She is very keen on staying healthy, especially as an athlete. It is a battle I chose not to fight because it is just 1 more thing the teen sees as mom policing her.
Maybe lay off the battle of policing her eating habits for a little while and see if something changes? As for stealing and hoarding food.. I would put a stop to that, not healthy at all.
Make sure she has healthy choices when she gets home from school.
Good luck... teen girls are not easy but it is worth it in the long run!!