There are folks in this world who will excersize any power they get. Sad you were at the other end of it, but happy she did relent.
I would like to think that the librarian meant well, but was misguided. Our school district just came out with a policy that large groups of kids will not be accelerated in math but will instead be kept in heterogeneous groups because the high school math teachers complained that even the accelerated students were arriving unprepared. I think that has more to do with the Everyday Math curriculum than any disadvantages of accelerating. I don't think the district is intentionally exercizing their power to disadvantage gifted kids, but doing what they think is best and responding to parents of kids who complained that their kids were being pushed too hard. Maybe same situation with the librarian who hasn't seen too many kids who could handle that level of material and was trying to prevent "frustration".