Be aware that eating carbohydrates (that means bread, chips, potatoes, etc) is essentially eating sugar. And your body responds by being hungry!
It may be that she is hungry! Frankly, eating a sandwich and chips isn't likely to fill her up, but make her more hungry, unless there is a good amount of protein in that sandwich. You said that you keep only healthy foods in the house and don't allow soda, which is fine. But what about protein? Is she getting an adequate amount of protein each day? I LOVE food! but if I eat an adequate amount of protein at my meals, I am too full to eat more than a bite of anything dessert-y, and certainly too full for much in between meal snacking. One ounce of meat protein (one ounce of tuna for example) has about 7 grams of protein. One large egg has about 6 grams of protein. 2 frozen waffles with syrup MIGHT have about 4 grams of protein, but all the sugar in it (carbs plus syrup) makes the insulin flow and the result is hunger.
Eggs have been much maligned over the years b/c of cholesterol. They are one of the healthiest foods. Have your daughter eat an egg or two (scrambled, fried, boiled, however she wants... make them into an omelet!) and a slice of whole grain toast for breakfast. Add a piece of fruit if you want (half an apple, some orange or grapefruit sections, a banana: just make it whole fruit and not juice, which is LOADED with sugar)... and she will not feel hungry for HOURS. Why? Because there is adequate protein, and NOT a sugar rush from simple carbs. All her meals should follow that pattern. Lean protein (if she will eat 15-20 grams of protein at 3 meals a day, she will NOT be hungry), high glycemic index complex carbohydrates ( WHOLE grains, not highly processed ones like regular pasta, boxed cereal, or rice/potatoes are) and WHOLE fruits (meaning not apple juice, but an apple; not orange juice but an orange) and if she DOES feel a little "snacky" eat a handful of healthy nuts or low sugar yogurt (like the greek yogurts): walnuts and almonds are excellent nut choices... then she will be giving her body what it needs. Any green leafy veggies she can eat to her hearts content, and brightly colored fruits & veggies are packed with vitamins/antioxidents and bioflavinoids, etc and are LOW in sugars (red/orange bell pepper, carrots, tomatoes, raspberries, blackberries, blueberries, strawberries, etc).
Chips make you hungry. They are totally empty calories that break down to sugar in your body. Plain white bread is exactly the same.
Now, there may be some emotional issues going on with her that is making her eat like she is... she is at a turning point in her life: she's about to be an official adult! Just that alone can be extremely stressful, even with great support systems in place and for emotionally well-adjusted kids. She is approaching one of the biggest transitions she has ever faced.
But, if you help her/provide her/guide her to the proper mix of food choices... even if she DOES use food to manage some of the stress, then she will not be ABLE to eat much junk. She will be FULL.
Most people do NOT eat enough protein. It doesn't have to be steak or beef. Fish, chicken, turkey, cheese, eggs, nuts, beans (we love black beans at our house!). These ALL are good sources of protein that you can play around with and incorporate into your daily diet without a drastic change.
I say all of this because you said that you have never made an issue about her weight. That's fine. But you didn't really say what you have taught her by example, other than that you don't allow junk at home. That is very vague. And everyone's definition of junk is slightly different. Canned fruit might sound healthy, for example, but I'd bet it is packaged with syrup in the can and if you read the label is probably far from the healthy picture you might think.
And 5 tacos for breakfast? I'm guessing it was drive-thru also? How unhealthy is that?! Our 12 year old and 9 year old started reading cereal box labels themselves this past summer, because we pointed out to them that what they were asking for (sugary cereals for breakfast) weren't healthy for them to eat every day. Sure, it's okay once in a while... but not every day! When we explained it... they were quick to NOT want the cereal. And our son eats a LOT of salads instead of fried stuff. Or grilled chicken sandwiches instead of fried ones. You can't just ignore the whole issue of food so that you don't make it an issue for her. You have to provide her with information about what is healthy and what is not, and why, and then guide her to healthier choices when they are available. Not by being overbearing, but like you would teach her about other unacceptable behavior: "Can you think of a better way to handle your anger than hitting?" = "Can you find something else on the menu that is a healthier choice?" "Can you think of a different way to serve/prepare that so that is is healthier/better for you?"
hth