Yes I did. He was failing at his mocks. Struggling with all the things you outline. He ended up with excellent GCSE results and got 100% in some of his papers. It was very labour intensive though for me!
I bought loads of revision books and put together a revision plan for him so that all subjects were covered. I planned in plenty of breaks including daily breaks for getting it side and exercising (aerobic exercise is fantastic for ADHD).
I made him do his revision in the kitchen with me. For most if it I was literally sat with him (I didn't do much else for the period!) . He needed that to ensure he revised and remained focussed.
I did all the sorting and organising for him so he had everything ready for the revision. To avoid issues like you describe when they can't find pens, paper, books, notes etc. Take that out of the equation, become their PA!
I printed off tons of past papers. Marked them, went through the answers with him. Got him to redo to them. I think this is what got his exam technique down.
I constantly reminded him to read and reread the question. And not to start until he was sure he had understood the question. For longer answer question I reminded him to go back to the question and check he hadn't gone off at a tangent. I reminded him of this repeatedly and as he went into each exam.
He was also helped however by the fact he had a prompter for his exams. And part of what they can do is help stop students getting distracted and prompt them to make sure they've read the question properly. He also got extra time in exams and was able to take beaks. Obviously with no diagnosis you may not be able to access any of that but ask the school and check if they can apply on the basis of her difficulties/needs. Do you have the means to access a private diagnosis prior to her exams?
Doing all this basically taught him that revision was important (he struggles with cause and effect) and how to revise.
He therefore did much more himself at A level and then did all his degree revision on his own.
There was lots of stress and tears at times (for both of us!!) as obviously he didn't want to be doing all that but he now tells me that looks back on that period as a really positive thing that I did for him.
The driver for me was that I couldn't bare to think about how he would feel if he opened his exam results and had failed everything. He is really bright and would have been devastated. I just couldn't let that happen.
I'll just add here that I also have ADHD so the above was super challenging for me too....but once I am hyper focussed on something....