Have you talked with the teacher about this? I think if they are going to insist that she read at her Lexile level, then they should also help her find appropriate books. It seems really silly, a case of following the letter of the rule and missing the spirit. The idea is to help people improve their reading skill by reading "just right" books. In your dd's case, there seems to be little need for her to improve since she has already reached a level higher than most adults.
And of course, even very few college-educated adults read college level reading material on a regular basis. I would hazard a guess that very few mystery and fantasy novels would meet this lexile requirement. And even most literature read in college is probably not a 1550. My only suggestion would be non-fiction and have her read journal articles on a subject of interest to her. But that may not appeal to her at all if she is looking for fantasy fiction! lol
Sorry we're not much help here. I would go to the school and insist that they either provide appropriate reading material or change their requirements.
