It sounds like your emotional reaction is what is feeding her. Im not saying this is a conscious thing on her part.
She gets cross and then you give her attention, either treats (bribes) hugs and soothing or snapping and shouting.
It might seem to you that these are different reactions and she should choose the nice ones and avoid the nasty ones, but its all the same to her. She has created excitement and got your attention.
Stop engaging. Stop reacting. Stop giving choices. Just do the same every day, same breakfast, same routine, same amount of oversight and reminders (You will know what the reasonable amount of this is based on her abilities)
Then when she huffs or shouts, just go “oh dear, hmm, ahhh, sounds tough”. Let her vent but dont feed it. If she doesnt get ready, take her to school in pajamas and without breakfast. (At least have that as your mindset) BUT no shouting, ranting, pleading, blaming, shaming....just matter of fact “OK DD that is what you chose” in a quiet voice.
If you struggle to not rise to the provocation, try playing DD morning bingo to yourself. One point for every rant you predicted. If you get five points you get a chocolate after she has gone into school.
Remember she will escalate the first few days as she will crave the excitement the two of you have both been generating in the morning so will get even more rantish if you stop reacting. Just stay the course.
Then to give her a little something to look forward to, as she adores reading, can you get some audible books to listen to in the car (or on headphones from your phone) on the way to school. If possible make it seem like you are getting the books as something for you. Dont big it up, just start one morning, again its not about a reward or bribe, its just something you are doing FOR YOU to have an enjoyable moment with her.
Oh and hold on for the teenage years, you will probably get through it now, but its coming back when she his 14 ish, so you really need to practice your not engaging as that age is a complete whirlwind. 🙃