Hi E.,
We have gone through this with various family members, and I too have 'brain fog' at times (what we call it in my family) so I get the need to have someone with you at appointments.
What I do is have the doctor write it down. They will do that. I come out with lists, diagrams, post it notes ... encourage your daughter to get them to do this. They just need to be asked. Take a back seat.
I then take those notes, staple to the sheet that I get for appointment (reminder) and this goes on my cork board in my office. It sits there until I'm ready to file it.
My sister prefers a binder (for my mom).
Do whatever works for you (or in your daughter's case, for her). She should now own it.
Have an excel spreadsheet (or whatever system) with one tab for doctors, with pertinent info. One tab for meds (which doc prescribe/what pharmacy/what for etc.)
Have your daughter own this and update once every 6 months. You can 'share' this with your son.
Have her help with meals - first thing in morning. Owning this will empower her, and give her energy (mental). Making life as normal as possible is energizing. When I'm having a rough day, I get everything I can do done (sometimes not a lot) by 10 am. I putter. Hope that helps. When you feel you've accomplished something (even if small) it changes the outlook for the day.
Same for appointments. Ask to schedule them for first thing. Mine are first ones of day. They will do this for you - brain fog is minimized in morning usually. If meds make brain fog, then try to time it so that she's alert.
She should 'own' this as much as possible.
It's only really when cognitive abilities decline (dementia) as opposed to 'brain fog' and fatigue that you need to step in a lot. Rest and puttering is *hopefully* do-able with brain fog and fatigue if she gets into a routine. Then she can own more of this and you can start to back off a bit. Independence will follow bit by bit. (if her condition worsens, etc. that's something to address later on, but see how these steps go). Hopefully she adapts to it well.
Hopefully that helps. It works for us. Good luck and keep us posted :)
ETA: I get what Ziggy is saying, and hope I didn't come off as insensitive or suggesting you've been negligent. Not at all. Every case is different (everyone is unique) and I don't know your daughter's situation fully. She may find it very taxing and it might just be way too much at this point. I myself have my husband handle all the taxes, etc. although I am trying to get back involved with this - at least sitting in, so that I have a clue. Initially, it's easy to hand your life over to others while you're trying to grasp that you're not well (which is draining enough as it is). Over time though, taking back ownership a little at a time, is a really good thing - whatever she is able. It is huge for self esteem. Feeling powerless (medically) health wise is so .. tough. Feeling dependent on others .. horrible when you're an adult. So that's why I'm encouraging her to take ownership where she can.
Remember, there are so many people who don't have the benefit (luxury really) of having a 'you' to help them. Doctors and medical professionals (pharmacists, physiotherapists, etc.) will help .. let her ask them for help. She can even ask them to speak clearly their instructions and she can record it on her phone. It's do-able.