First off, you are welcome in the 2E forum. "DD" means "dear daughter," (or sometimes another adjective, given the erratic behavior of some of our loved ones).
It sounds like so far, you are doing everything right, and your principal's email sounds promising. One suggestion that I would make to help bridge the gap between high-level understanding and low-level reading is audiobooks. I wouldn't spend a lot of time talking about her test scores or filling her with the idea that she's smarter than her peers, and I probably wouldn't do the grains-of-rice demonstration, certainly not before school starts. Instead, "feed the beast" by giving her the information and answers to her questions that I'm sure she craves. If her friends at the new school have all plowed through Harry Potter and she wants to know what they're talking about, then check the Harry Potter audiobooks out of the library (they are excellent!), and let her listen. But don't manufacture problems before they appear. Maybe no one will care about Harry Potter and instead they'll be playing Percy Jackson, or ballet school, or who-knows-what.
