Hi, K. --
What you're going through sounds quite a bit like what we went through with my daughter from the time she started sleeping in her crib until she was about 2.5. She's now nearly 3.5, and sleeping is no problem at all.
You sound to me like an analytical, intelligent person... you've covered your bases, considered all stimuli, explored the physical, aesthetic, and psychological, and you've tried to create a routine, a structure, and an environment. What else could there possibly be, right? We did the same thing and could also ennumerate every article in her bed and/or routine...
So, the only thing I can suggest that might help is to do just the opposite of what you're currently doing, or modify it in an unexpected way. We found that, over time, our daughter would tend to "outthink" the routine and the expected structure of things would actually come to be an obstacle to sleep. I know, that sounds nuts, but, I believe, for some children -- especially creative, mentally energetic types -- there's a compulsion to push the boundaries of routine.
So, when I would see that trend coming on, I'd change things up a bit so that my daughter would have something that she had not yet figured out how to predict or correct for.
What I'd suggest for you is that you create a new ritual, and involve your daughter in its creation. I think this is a powerful way for her to become confident that she is in charge of her ability to sleep. Remove everything from her bed. Remove the scents. Change the bath scent. Rebuild the ritual from the ground up. Don't deprive her, but surround her with the minimum necessities. I feel from what you've related that perhaps your daughter's saturated with stimuli. Maybe she's more mentally and physically sensitive than you can realize, and so many things (scents included) for her to process and be surrounded by could be preventing her peace rather than bringing it into being.
Also, obviously, she can sense that you're hurting for her and with her over this. I'd suggest for you what I have had to do with myself... get off by yourself for a few minutes before going into bedtime battle and center yourself. Be confident that you can help her find her rest, and convey to her that you're confident in her ability to find her rest, too. She needs to turn off that little head, so the fewer the distractions or food for thought, the better.
When I was in college, I was so keyed up all the time, I could scarcely sleep, even when I was exhausted. When I would start to think of sleeping, I would immediately feel stressed because I knew how tired I was and wondered if I'd have the energy to get up in the morning when I needed to. Then, the longer I could not fall asleep, the more stressed I would become, knowing I'd be that much more tired. And, thus, the viscious cycle continued. I don't think I ever discussed this with anyone, but, if I had, I bet someone could have helped me by teaching me techniques to calm myself, control my thoughts, and put my worries aside. It sounds like your daughter is going through this in her own kid way.
Maybe, for a little while, rather than reading a book, you could do some very basic yoga - stretching, centering, things to help the mind relax rather than getting it going, as a book might cause it to do. Then, when she's got a handle on letting her mind go to sleep, you can reintroduce the reading part of the ritual.
I SINCERELY hope these suggestions help. We analytical people have a whole list of things we desperately want to do RIGHT, in a very specific way. We want to figure things out and create a plan. Sometimes, we have to see the bigger picture - that these little people are being bombarded by images, sounds, scents, concepts, emotions, and other stimuli all day long -- and it's exciting... maybe too exciting to filter out what's not needed long enough to shut down for evening repairs.
Take care,
H.