I don't have advice to offer on the school situation, but wanted to respond as your dd sounds very much like mine. Our dd was extremely talkative at home and thus the center of the household from a very early age, but did not speak at all at preschool for the first year.
She did start to speak some at preschool eventually, but even in 2nd grade we heard concerns from the teacher that she did not socialize much. By then I could discuss it with her and she explained that there were no social problems or anxiety - that she just preferred to spend recess in her "mind world." At that point, I started to defend her in the face of anyone who wanted to "fix" her social skills -- "As an hg+ kid, she doesn't have as much in common with the other kids in her class, and *she* is okay with that, so please don't try to fix her."
She is now 11yo, in 5th grade, still talkative and the center of the household. And although the social scene is still not her main thing, she has become very socially capable. This weekend she will be performing (as a member of the youth choir in our town) in Pirates of Penzance with the local opera -- I am very proud as it shows how far she's come.
I realize each case is different, but in this case, given time (years!) to get comfortable in a school situation, what once seemed like a scary problem has faded away.
Wishing you all the best
