If you say "in a future behind a glass dome", the immediate assumption is that this story takes place in our world. To suddenly introduce a River (I'm guessing River rather than Rover) God felt very unnatural. It was only then I looked at the genre, expecting to see SciFi, and saw Fantasy.
Does she have to venture out of the dome to get to the River God? Or is this inside the dome still?
The protagonist should be the one who brings the earth back its former glory. It seems that, at the moment, our hero does all the hard work only to hand act 3 to a new character to finish off. I need more info to understand what this seed and the river god have to do with restoring the world. As it currently stands, it's not even made clear that the world is in a bad state, only that mankind (I assume it's mankind) lives in a dome.
What happens if she doesn't do this quest? I'm seeing similarities between this story and Moana - both stories have a girl taking a small object to a god. In Moana, she MUST take the heart of Te Fiti back in order to stop the spread of the darkness which is damaging the natural world which they rely on to survive. So why MUST your girl go on this quest? In Moana, she was chosen by the ocean to carry out this quest. Why MUST she be the person to do this?
You've called her "optimistic". What's her arc? Where does she go from here? Is it better that she's pessimistic about her future and changes her mind over the course of the film?
I love a good fantasy adventure quest film and fantasy loglines are really hard so here's what I would do:
- Expand on the world in which the plot is set. Be a little more explicit so we understand what's at stake and why it's important.
- Clarify where the quest takes place - out of the dome?
- Tell us why this seed is important. How does she know that she must take this seed to the river god? In Moana, Gramma Tala opens the film telling us (the tribal children) the legend of Maui, Te Fiti, and the heart stone. What's the legend here? Where is that exposition going to come from?
- Tell us why it MUST be her
- Tell us what happens if she fails
Hope this helps in some way and I look forward to seeing the next version.