a young rain-maker must quickly master her abilities to save the kingdom from the Ruler of storms
Her goal shouldn’t be to master her abilities. It should be to stop the Ruler of Storms from destroying the kingdom. Mastering her skills is merely a stepping stone to this.
Why her? Why is she the only one who can stop him?
As Richiev pointed out, you also need the incident that sets this story in motion.
To help create a three dimensional antagonist maybe consider giving us his motives for destroying the kingdom. I feel like I need to know a little more as to why. Not only does this flesh out the story but also adds to the protagonist’s character and motivation.
Hope this helps.
As the others have said.
It’s not clear what the main action is, what she is supposed to do. If she’s a rain-maker, is her goal to bring rain that the “Ruler of storms” has prevented from falling? Or his her goal to prevent this “Ruler’ from inflicting too much rains, causing destructive floods? What’s the principal dramatic problem she must resolve?