I hear and understand your frustration!
~My youngest son's best friend (they are 5) is WAY brilliant...like WAY gifted! He taught himself to read at 3, does serious math in his head and is a little sponge about learning! His handwriting is impeccable, he taught himself to play piano and LOVES sports! Anyway, they have been in 2 yrs of preschool together and this next year will be entering K together. In our area, they do not do any thing for gifted kids until after the 3rd grade, when and only if they have past all the 'gifted' tests (1st grade, 2nd grade, 3rd grade) his mom, like you, is worried about him being challenged...her plan is the same as what she has done throughout his preschool career...she sends extra stuff to school with him, for him to work on when he is done with the regular assignments. Sometimes it's workbooks, some times its college age math books...whatever his lil' brain is currently focusing on at that time in his lil' life. It works for them. Maybe it will work for you?
I can not tell you how surreal it is to walk in to talk to the sweet lil' boy and have to be like 'Sorry buddy, I don't mean to interrupt your reading of the mechanics of rockets...or the latest issue of popular science :) My friend is used to it and got many a pointers from her MIL, apparently her husband was like this as a child also, very independent learners who need absolutely NO outside help as far as being 'taught' things!?
I wish you all the luck! I am with you on your thinking about keeping her challenged and letting her continue to learn and grow at her speed!!
Pft! To the librarian! What the heck? That woman sounds frustratingly dumb!