Stop with the high expectation for the FL, I mean she doesn't even remember her mom or even dad, was locked up till her death and has no clue what's outside that cabin she lived in. And because of her being unfamiliar with many people she get scared easily which is reasonable because of the abused she received. After her previous death she got traumatized causing her to fear darkness and fire!
She is actually cool enough to escape from the beginning and now. Also even though she believed she's unwanted by the Duke because she's not the real child (she is tho), she trusted them! And with that-- WE HAVE A STRONG FL!!!