How can I deepen a fantasy protagonist's growth and agency believably?

[JustinRT]

I'm writing a fantasy novel and I've hit a wall with my protagonist; she has a compelling backstory and a clear goal, but she feels flat on the page, reacting to events rather than driving them. I want her to have a meaningful arc where her cynicism is challenged, but I'm struggling to show her internal growth through her actions and dialogue in a way that feels earned. For other writers, what techniques or exercises have you found most effective for deepening character development? How do you balance giving a character flaws that are relatable but not frustrating, and what's your process for ensuring their choices are consistent with their personality while still allowing for transformative change?