What an interesting update. I have one who loves to learn, but only on their own terms. And always prefers to be invisible in the class. They could not bear to "fail" but are absolutely without interest in teacher pleasing, or in being "the best", in fact actively avoid being noticed for doing well. This make school really tricky. I really related to this :

"with the thought that it might be a long-term solution for a kid who seems to want to blend with whatever she sees her age-mates doing if that maximizes her opportunity to play with them."

I think that this is an incredibly powerful observation you have made, and you have described it delightfully without judgement:

"The teachers were warm and communicative and calming and great at identifying the social-emotional areas where she seemed to need to work. It just seemed a little bit like she was trying to bootstrap open-ended buddy play and silliness into an environment organized differently. She told me that she liked receiving lessons from the teachers but didn't like doing the work afterwards. From what I could figure out the lesson presentation was social interaction and then practicing the work felt isolated. When I observed the class I saw another new student who was responding very differently, diligently practicing with the materials until presented with new lessons, moving through work and work sequentially with great joy. At some point she and my daughter were both given lessons that allowed them to do a spelling work. I saw the other student repeatedly get the work out, follow all the steps, and put it away. My daughter used it once and spelled the words then apparently repeatedly declined to do it again when it was suggested to her. While I was observing I saw them suggest it to her. She took it to a table and kind of half-heartedly pretended to be looking at it when teachers came by but was really focused on trying to get out a stool and move it to someone else's table and kept having to be redirected."

There are many things to learn about your daughter, and teaching environments in this passage and you will doubtless be able to reflect back to this many times, hopefully in ways that help you help your daughter.