We had three children, about two years apart, and our eldest has ADHD as well… I think life with toddlers is chaotic under any circumstances, and the toddler years were definitely crazy for us!
My hubby makes me sit down and come up with the checklists. Then, for bigger projects, he has me break down the list into mini-checklists, so each step has to be checked off. Then he goes over the lists with me to make sure they’re practical (I’m not so good at practicality).
For example, you mention that your wife needs to get treatment lined up for your daughter – you can help her get a checklist set up for the project, including every tiny detail (e.g., find counselor, make appointment, etc.) and then print it out in a monster-sized font and post it on the fridge (or some other obvious place where it won’t be lost or buried)… explain (again) that it is very important (which she probably knows – I know from personal experience how easy it is to be distracted away from projects, even when I know how important they are) and explain that it’s super high priority, even more important that getting the dishes done… Then when your two-year-old interrupts her as she’s proceeding with arranging your daughter’s treatment, she can later look at her checklist and jump right back into the next step (hopefully, instead of diving into some other project).
It’s okay to feel frustrated. It’s even okay to express it… My hubby and I found therapy to be helpful. He learned how to tolerate my idiosyncrasies a bit more, I learned how to develop a tougher skin so I could accept constructive criticism a bit better, and we both learned how to communicate better – our minds run in different tracks, so learning to communicate is important (I’ve learned that telling him, “The thingie is on top of that big thing in the garage,” does not help the average person find a tool on the workbench)!! It helped a lot… Good luck!!!