I'm sorry you are feeling discouraged. I certainly understand. I am currently working through MFW K with my 6-year-old autistic son. We started in Aug. 2014, did his K work 3 days a week through the school year, took a break during the summer, and continued with it this school year, doing it 4 days a week. He will finish K at the end of January and start 1st at the beginning of February. I am planning for him to take 1 1/2 years for K and 1 1/2 years for 1st and see where he is after that. My son has ST and OT from a private therapy provider, and we do not do school with him on his therapy days.
That being said, our focus with his K work has been a bit different than it was with my 2 older daughters, and I "tweak" it to fit his needs. My son, like your daughter, is very smart academically. He taught himself to read, he knew the letters and sounds before he even started K, he knows numbers into the thousands, etc. So, academically, K is not a challenge for him. Things that ARE a challenge for him are sitting still and focusing for a period of time, listening to and following directions, handwriting, making some of the letter sounds (speech delay), formulating answers to questions, sitting and listening to stories read to him, etc. So, my focus for him this year have been the Bible/character lessons (learning his Words to Remember and learning about Jesus), learning to sit for a period of time and gradually lengthening that time that he can sit, learning to write his letters and gradually writing whole words, sitting and listening to a story read aloud to him each day, etc. Those are just a few things.
When you do feel your daughter is ready for K, here are some suggestions I have for you. Just take her where she is. Eliminate some things from the K schedule if the day gets too long. You don't have to do everything. My son is not an artsy kid and hates getting his hands messy, so we skip much of the art and coloring activities, but I've been working with him on cutting and pasting and getting used to having glue on his fingers without him having a meltdown about it. He's come a long way with this!
Decide what your focus is for your dd, what you desire for her, and work on those things. For handwriting, we spent at least the first half or 3/4 of the school year last year just writing his letters in a salt tray and not using pencil and paper at all. I ordered the program Handwriting Without Tears for him, and now he writes his letters first in a salt tray and then on a chalkboard. Eventually he does it on paper with a pencil. But it took us quite awhile to work up to using paper and pencil, and that's okay. He certainly has not yet written a complete sentence...just letters and words. To start, I had him only sit for maybe 10 min. at a time and then he got up to take a movement/active break...jumping on his mini trampoline or running around a bit...doing something active...and then I called him back to the table to work on more seat work. Gradually increase the time you require your dd to sit and attend to the task at hand.
I had debated waiting to start K with my son until he was 6 (that would have been the beginning of this school year), but my dh and I decided to start him last school year, when he turned 5, because cognitively, he was ready, even though he was delayed in speech and fine motor skills, among other things. I didn't want to hold him back. I wanted to take him where he was at and work with him there. It turned out to be a good thing to start him when we did and just work through it at his pace.
So, again, when you feel like your dd is ready, choose 2-3 goals for her and you can use the K materials to achieve those goals. My son's K experience is completely different from the experiences my 2 older daughters had, but that's okay. I need to work with him where he is at and not force him to do too much before he's ready. Definitely take the time you need to work through her health issues and behavior issues, but you can certainly use the K curriculum to help you with some of that. The character lessons/Words to Remember/Bible lessons are great for some of those behavioral issues. The K materials/activities are great for teaching them to focus and follow directions. Don't feel bad about tweaking it to fit your daughters needs.
Hang in there! You can do this!