Looking for advice on my daughter's eating habits

I have two stepdaughters, both in their early teens.We eat breakfast, they take a lunch to school, when they come home from school we have a snack, we have dinner at 6, and a little snack around 8.Younger SD basically only likes junk food, peanut butter, bread, cheese, and chicken. She doesn't like any vegetables, fruit, legumes or grains. She gets a monthly allowance, and spends all of it on food, usually things like Pringles and Doritos. She can easily eat two full-sized cans of Pringles in one sitting, which is about 2,000 calories in processed carbs. Sometimes after-school snack might be a sharing bag of chips, split between 3 or 4 of us (depends on who's home) - and if she has the money she'll still get a can of Pringles and eat that along with the snack we've provided. The snack time after school is the only time they can eat food they've bought, because other meals and snacks we've specifically prepared food, and want them eating what we've prepared. I don't understand it, because if I eat a half can of Pringles I'm starting to feel pretty crappy. She never seems satisfied unless she has a lot of what she wants.If she doesn't have the junk foods she prefers, her appetite isn't diminished. As a snack she can still easily eat 6 slices of bread with peanut butter in one sitting, or a couple of grilled cheese sandwiches. If I say, for example, "That's a lot of bread," she'll put one slice back in the bag and still have 5.If left to her own devices for meals, say if she's off school and me and my wife are at work, she'll buy herself chips and she'll just eat those for a meal.If she gets money for her birthday or something, like from a grandparent, she'll immediately leave the house and go to the store to buy junk food.For her past two birthdays, instead of having a birthday cake she has requested chips. I realize that, on balance, chips are probably actually healthier than cake, but it's just the principle. :pShe regularly has an upset stomach, but can't seem to make the connection between that and what she eats.Lately she's been complaining of pain in her chest, which she was worried was a heart attack, because she knows she doesn't eat very healthily. So we took her to the doctor, who said her heart was fine, and that it was probably likely indigestion. She's made some small effort to eat more healthy over the past few weeks - if we have salad for dinner, she eats one bite of lettuce and obviously doesn't like it.She's mildly overweight, like maybe 15 pounds. She doesn't seem to be getting any more overweight, she's been about the same level of chubbiness for years. I'm not concerned about her fat at all, but I am concerned about her internal health.Part of it, I'm sure, is that she doesn't like many foods, so a lot of the time she doesn't get as full at dinner. So, let's say we have a meal that's chicken breast, corn, and mashed potatoes. Of that, she only likes chicken, so that's all she'll eat. Or we might have spaghetti with garlic bread, but she only likes garlic bread. Later, she's obviously going to be hungry. She's always asking what's for dinner, and nearly always being displeased because we're having things she doesn't like. A couple days a week we'll make a meal that is mostly things she likes, but we can't do that all the time, because we're interested in serving and eating a variety of healthy foods.Dinner is ready within the same 30 minute window each day, but every day as it comes towards that time she's asking "When's dinner?" "Is it done yet?" etc. Sometimes it makes her seem obsessed with food.Older SD of course also likes junk food and sweets, but eats a much bigger variety of other foods, and rarely eats a ton of junk food all at once. For her, a typical lunch might be a single serving bag of chips, grapes, an apple, carrots, celery, crackers with cheese, and a glass of milk. I don't understand why they're so different, although I do of course understand that people are just different from each other.We've talked to her about she feels about what she eats, and she says that a lot of the time she feels bad/guilty about eating the way she does, but does it anyway. Feeling that way must make eating pretty crappy sometimes, and I feel really bad for her.About 6 years ago, we tried restricting snacks to things like: 1 thing from the sweet box (like a cereal bar) + 1 thing from the savory box (like a pack of chips or crackers). At that point she also didn't yet get an allowance, so she wasn't buying her own snacks. We did that for probably a year, and she still binged whenever she had access to a larger amount. We could restrict like that again, I guess, and it would reduce her junk food intake, but it wouldn't solve whatever the underlying problem is.We read things saying that her eating that way may be because she feels like she can't get enough food that she wants, and worries it'll be taken away, so she eats everything while it's there. I don't know how true that is, but we thought, whatever, it's worth a shot. We gave her unlimited access to all foods she wanted. On an average day after school, she'd have 10 single serving bags of chips as snacks, or one like every 30 minutes, plus a few snack bars, bread, etc in addition to dinner. After four months of that, with her appetite seemingly unsatisfiable and also getting fairly expensive, we gave up and moved to our current meal/snack routine, which we've been doing for almost 3 years now.My wife and I set a good example. We eat a variety of foods, almost always homemade, plenty of unprocessed fruits, vegetables, grains, fats and proteins. The only time we have junk food is on Friday, which is our family movie night, and even then we make our own pizza to go with it. Yes, we are her parents, and we could just force her to not eat junk food at home, but I believe that would just push the issue away instead of resolving it, and of course would not affect what she eats outside of the home. We want her to grow up having a good relationship with food. It seems like she has a bad relationship now, and I don't know where to go from here.I guess there are a lot of questions in here, so I'll break it down:Has anyone else dealt with something like this before?Should we be worried about the way she eats?If so, how do we get it to change? How do we find out what's causing it?Specifically, how do we get her to eat a bigger variety of foods?Secondarily, how do we get her to eat more reasonable portions of junk foods?(crossposted to r/eatingdisorders) via /r/Parenting http://ift.tt/28QxDkW