Hi and welcome to the Chiari forum.
WOW, I am sure you are feeling a tad bit overwhelmed with all you are going through.
My I suggest something that has recently come to my attention....have your daughters Drs check her for any tongue ties...it can affect those with them in very odd ways, and in some newly read research my daughter and I have found that it can be related to not only Chiari but to autism and ADHD....and a few others as well.
As for how to tell if your daughter is feeling pain wise post op....try having her explain pain while doing a task, such as lifting heavy books.....hold three is ok, but 7 books is too much....she may do better saying I can hold this many but not that many....having Chiari it can hurt to lift or hold heavy items....just an idea. But do it prior to surgery should she be a candidate for it...so she can get used to lifting the books and saying which ones she can hold.Then do it post op, or ask how many can you lift...it should give you an indication of where she is pain wise.
I hope this is helpful.