How to turn a sheltered scholar into a believable, decisive leader?

[NatalieS]

I'm outlining a fantasy novel and have hit a major block with my protagonist's character development; she's supposed to evolve from a sheltered scholar into a decisive leader, but her internal motivations feel weak, and every plot event I devise to force growth seems contrived, making her reactions feel like plot devices rather than authentic choices stemming from her personality. I have pages of backstory, but it's not translating into a compelling, active character on the page, and her voice gets lost amidst the world-building. For fellow writers, how do you bridge the gap between a character's biographical history and their dynamic presence in the narrative? What exercises or questions do you use to uncover a character's core contradictions and desires, and how do you ensure their arc feels earned through gradual change rather than sudden, unconvincing shifts prompted by external events?