To save the Tree of Life from the ever encroaching shadow, a girl must learn to once again trust in humanity. The very people that wiped out her entire kingdom.

"When the shadow engulfs a neighbouring farm, the forest nymph must save the tree of life, overcoming her distrust in humans"
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But why should she?

A similar premise took place in Miyazaki's "Princess Mononoke (1997)". What makes your plot unique?

Also, the stakes aren't clear.
What if the Tree falls?
aka., what's her dramatic need? As a result of which, what becomes her objective-visual-goal?

Good Luck!!

Some good points from CraigDGriffiths and Richiev. Also it's not 100% clear what the inciting incident of? your story is. What is the "ever encroaching shadow"? Could it already be infected, ie wilting, and therefore show to the audience that something has happened?

How does trust humanity look like? That is the conclusion the audience will draw. So how will you demonstrate that? Does she have to trust a person, which would be an allegory for humanity? Loglines tend to display plot as a way of showing emotion.

Goal: Save the Tree of life
Action: Learn?to trust humanity

How is that shown on screen??
Is it two hours of your lead character saying, "I will trust humanity, I will trust humanity?"
Maybe she reads some books on the good side of the human race.

Also, how will learning to trust humanity (Supposing she succeeds) translate to saving the tree of life?