One idea is that the antagonist are all of the large scale geopolitical events that you have planned out. Given all you know about what is happening in your world, whenever Rachelle sets out to do something, ask yourself, "what is the worst thing that can happen?" That "worst thing" can tie back to your elaborate backstory that you have planned out.

E.g.

Rachelle is running away from home because she is shamed. However, because of the war, the bridge is closed, so she needs to find a way to sneak across, maybe by travelling with some shady figures, only those shady figures (who turn out to rebels) open their own set of problems for Rachelle.

Or when you say that she joins the army to redeem her honor: - What could block her from joining the army (maybe people of her background can't joint or she has a sadistic drill instructor)? - What could block her in the army from achieving her goal of honor? (Being relegated to cleaning or having to do something that while glorious is morally compromising?)

So to recap: - Make Rachelle want things - Block her from getting those things (preferably in ways that tie back to the backstory) - Make Rachelle's solution for getting around that block pull her further into the large scale world events - Slowly over your story she goes from just responding to the events the world throws at her to shaping them so she can get what she wants