My DS8 also is a crazy good reader, and has a requirement to read 30 minutes a day, but there is no restriction on what he reads. We do send books to school with him from our local library, since the school library, while prety well stocked, doesn't have exactly what he wants.
It takes us time to find things that DS will want to read, though we always feel lucky when we strike upon a series. Just my opinion, but I would ask the teacher if it's OK to ignore the lexile level business, since you all know your DD is an excellent reader, and just let her pick what she wants so she can get her love of reading back. I'm sure no teacher wants to be responsible for crushing a child's love of learning.
As for HP, that's great if your DD wants to read it again. DS read the first one, but wasn't overly excited about it and didn't want to read any of the others. I'm trying to think back to what I loved at that age... Did your DD read all the Anne of Green Gables books? How about the Chronicles of Prydain? If you get clearance for below lexile books, post again, and we can give a ton of suggestions.
