have you tried alternating with motrin? my youngest (14 months)recently had a bout with a fever that just wouldn't quit!! i was giving her tylenol at home, but it just wasn't doing anything. I took her to the ER at doctor's and they said they couldn't find anything wrong with her and sent us home.
the next night i took her to children's and the first thing they did was give her a size-appropriate dose of motrin. within an hour, her fever had lowered from 103 to about 99.6.
i dont know if this will help your little girl at all, but i would give it a shot. good luck!!!