The worst situations I find myself in always involve trying to figure out "won't" from "can't". And it's so much harder with teenagers*, when "won't" takes on a whole new life of it's own. It sounds like you may have a gooey intermingled mess of both on your hands - what especially caught me eye was:
I think secretly, she is frustrated. She makes general comments about herself that are not positive.
This to me raises the possibility that she might be all-too aware of the problem, but feels helpless to do anything about it. My own DS is the king of avoidance. If he (thinks he) can't do it, he avoids. Which
looks like he doesn't care, and makes his teachers mad as heck. When actually he cares so much it's just too painful to face, and so he acts like it doesn't exist. All the while (invisibly) hating himself for his failure, yet looking serenely indifferent on the outside.
What we are working on is trying to help him understand why, if he actually does care so much, his behaviour nevertheless sends the opposite message to his teacher. So he needs to
show his teacher that he cares, because as long as the teacher and I thought the problem was that he didn't care whether his work was submitted on time - or ever - we were trying to solve the wrong problem. Now (thank goodness we're on year 2 with this teacher), we are focusing instead on killing avoidance as a coping strategy for LDs, which means not just teaching him practical organization and time management approaches, but even more importantly, teaching him to communicate where he is at as well as when/ what feels too hard.
More practically, the biggest help for us has been electronic-based homework. We have a huge advantage of one teacher for all core subjects, and that teacher uses an electronic platform to assign and receive work. Unfortunately, most kids aren't so lucky. Still, if you can persuade your DD's teachers to accept electronic submission, you have a great tool for solving half her problems. (If you can possibly get them to post assignments electronically, a major bonus for the other half). When DS had to hand in paper, it mostly never happened. But now he just hits submit when he's done, and no lost documents, no forgetting to hand in. (And one electronic calendar where everything is.)
All this would undoubtedly be easier if your DD had an IEP, and was recognized by her teachers as struggling with real deficits, not just laziness. (For us, getting the teacher to see the problem wasn't "not caring", but rather avoidance because DS cared so much it hurt, was critical to trying to fix it.) So two thoughts on a possible ADHD diagnosis. (1) Make sure the tests used aren't biased to hyperactive/ impulsive issues (and typical "boy stuff"); inattentive ADHD looks really different, and girls are hugely under-diagnosed. (2) While ADHD and executive function tend to run together, the latter can exist on its own, and be thoroughly debilitating, so it's important not to over-focus on just ADHD. That said, I believe diagnosis is generally based on hitting problem levels in 6 of 9 criteria - and 7 of those criteria are about executive function. So take a good look at some inattentive ADHD descriptions and judge for yourself whether this feels like you are barking up the wrong tree, or need to push harder for the right kind of assessment. (Here's a decent overview that doesn't focus on younger kids:
https://www.additudemag.com/slideshows/symptoms-of-inattentive-adhd/)
And oh, how painfully familiar is:
DD has never really responded to rewards or punishment. I have taken away her phone, which is mildly effective, but also makes her sullen, angry, and withdrawn.
No great suggestions, alas. Even as a toddler, DS has never responded to extrinsic motivations or peer pressure. I do find, though, that even as a teenager, he (deep, DEEP down inside) actually does want to feel good about himself and the work he does, and if he can see the link between what we are trying to teach him and being able to do better, he does respond. Eventually. (Which, don't get me wrong, doesn't mean I am not getting yelled at every night to go away and let him do it himself. baby steps.)
But I do find it helpful to try to teach skills in a separate activity from doing a specific piece of homework, even if they are part of that homework. Ok, that sounds weird. An example would be "Before you start your homework, let's step back and think about how you're going to break down down this assignment into sub-tasks with milestones. Or brainstorm some ideas about how to structure that report." So we do stuff
before homework, rather than me interfering with him doing the assignment. We have broader, "strategic" discussions on the weekends about organizing and managing his workload (we're trying out Gantt charts this fall. Wish me luck). We brainstorm and set up diagrams or lists that help guide him during actual homework time without my direct involvement (which ranges from reminders to do a daily calendar check, to email teacher about anything causing him problems and at risk of becoming overdue, and to submit anything completed).
For this kid, everything is about building structures, and making every next step more obvious and explicit. We start with me building him structures, and over time are trying to make the shift to me guiding and prompting his structure building, and hope (some day!) that he will have enough practice to be able to build his own structures. (High school in 9 months, egad that clock is ticking loud).
Furthermore, if she's still getting the grades she wants, and positive attention from the teachers, then her opinion is: "Why bother?" And there's some legitimacy to that position.
For DS, avoidance was a very successfully strategy for a whole lot of years. He avoided stuff that hurt, to very little consequence. So we've had to attack this from both directions: (1) Make the stuff he's avoiding
less painful, so he can actually believe he can do it. But also (2) Make the avoidance itself
more painful. We've made it clear that having problems with the work is totally OK, but avoiding work is completely unacceptable and will have dire consequences. For instance, if he's struggling with an assignment, he will get extended time as long as he tells his teacher in advance, gets help, and if needed negotiates a new date (or possibly a change in the task). If he simply fails to hand in without such a discussion though, it's a zero and some painful feedback from a teacher he desperately wants to please. As someone who is self-employed, I have emphasized several times that this is the real world: if I take on a task for a client and timelines get messed up, or there is a problem meeting the original requirements, my clients will always be willing to sit down and agree on a new timeline/ task definition - as long as I tell them soon enough. But if I wait until the project is due, and then try to explain why it isn't done - - - well, I don't get paid and I may never work again.
As an aside, already twice this year he's gotten completely stuck on assignments that asked him to do something too hard (e.g. a story prompt that was too sad for him to cope with). Both times he insisted "It MUST be done this way, that's what the assignment says". Both times I (eventually) convinced him to come up with a way he could address the spirit of the assignment but in a way he could manage, and email his teacher asking if such a change would be ok. Both times, the teacher (who DS was convinced would absolutely say no), said "of course!" Again - like the real world. If you propose a solution when you identify a problem, people are usually pretty happy to make a change for you. Another 1000 or so times, and DS might figure this out...
* Tripped over a wonderful bit of parenting advice recently: "My main suggestion is to say, welcome to the magical world of living with a 13-year-old. Every parent of one chews wrong, laughs wrong, sets the wrong limits, and makes the wrong requests at least once daily, and is intimately familiar with indifference, hostility, indifferent hostility and hostile indifference."
