We don't use Lead 21, so I can't offer any advice there. As far as lexile levels, I found that (in spite of their aim to provide a true reading level not tied to grade), they often produced unbelievable results. I remember one of my dss scoring in the 1400s in 2nd or 3rd grade, and he clearly wasn't actually capable of reading or understanding almost anything on the list of corresponding books we saw!
Teachers also seemed to always come back to the "well, what if he misses something - grammar or spelling or something else not tested in lexile levels?" So, I think the best approach is to show a mix of "actual" work/reading from your dd, combined with her great lexile levels and MAP scores. I would bring in some books that she has read, maybe a few writing samples to show that she has at least beginning 3rd grade writing skills, etc... Maybe I'm just cynical, but I think teachers always use tests to their benefit - if your kid doesn't score high enough, that's proof that their not smart enough to need acceleration - if your kid scores really high, well, it's just a blip on the test but not "real life." So, I would ask for a conference-perhaps inviting the gifted coordinator and/or the student services coordinator as well as the teacher-and be prepared to show both test results and everyday stuff. I don't think you need to worry too much about appropriateness, because I'm guessing that the books chosen are screened for that in elementary school. And, if your dd is reading higher-level books at home, she's probably already reading about topics that may not be covered in the "normal" 2nd and 3rd grade books.
I would also ask (no names of course) about peers for your daughter. That really helped for me - "so, in terms of small-group work, how many other kids are at level X in reading?" (Don't ask "Are there other kids at my child's level?" because they always seem to respond "there are many advanced kids here at Sunnyside School!"). If they said, "Well, there's a range," I'd always ask, "So, if my child was in a small group of 4 kids, what would the other levels be?" One year, that question alone got my child working independently (which he vastly preferred) on much higher-level work, while occasionally joining in the next-highest level for some fun projects. There's no reason to have your dd spend her reading block on materials well below her level and there are lots of options for enrichment!
