think of it in this way, this story JUST started. she needs time to become strong. not every story will have the FL become instant strong and courageous. it needs time, which is honestly realistic and logical. technically it hasn't been even two days since she's been sacrificed, so it makes sense that she hasn't become mentally and emotionally strong yet.
I totally get you. I also avoided mary sue or shoujo type of FL. And I totally get where you coming from since usually this kind of FL would be so kind that you've become frustrated for her. I'm so frustrated with super naive and innocent FL where after all the abused and suffering she will forgive or even help them. Ughhh
I know she was abused but i can't stand female mc who is naive, innocent, and defenseless... i had my fair share of frustration with the happy-go-lucky japanese female shojo mangas and mary sue story which i would normally avoid. Now I'm just gonna stay here for the art. If she gets untolerable i'mma drop ╮( ̄▽ ̄)╭