Hi @Mimi-Simon congrats on writing a whole story and for having the courage to share! I enjoyed reading your story and I have lots of thoughts!
It really has the feel of one of those old fairy tales like thumbelina or the nutcracker, and it felt like you had the story figured out, now I would recommend editing it down while thinking about the journey you want to take the viewer on. Think of it this way, in 3-d animated movies they build the set models and the character model and the prop models and stuff, lots of building--but you don't put it all on screen. your audience sees the film through the eye of the camera, and its focus makes the movie.
there are some things that I think can be cut or simplified or re-ordered for a stronger story. think of your stories like this " once upon a time...and every day... until one day... and because of this... and because of this... until finally... and ever since that day... The end"
it is most effective to have 3 conflicts in a story, three attempts to reach the character's goal--two makes a pattern and the third (successful this time) breaks that pattern.
the strongest stories come from a clear vision of what you're trying to say and bringing the reader on a journey of growth and change with the character. right now it feels like your story is trying to say a lot of different things, so none of them get fully explored. You've got: nature heals grief, respects nature, girls can be brave and save people, and giants don't have to be the bad guys, and neither are strong magic guardian people.
What i would recommend for this is to write your story in as few words as possible. write it as a sentence, then a paragraph, then three paragraphs, etc. that will help you boil down what is the idea you are trying to get across and might give you ideas on how to use the other elements to be supportive instead of tangential.
The other thought I had, on another theme, is picture books are special. they get the strengths of words and pictures, which do different things. imagine you saw a picture of an apple that had the word apple typed over it. its a bit redundant. right now it feels like a written only story because you include so much visual information, which is true to the folk tales that were just oral or written like Grimms and stuff. I would invite you to make a version where you separate out the all the visuals as artist notes and see just how much it will strengthen your story.
So lots of thoughts, I hope it is uplifting and not overwhelming. the basic recap, it's got a lot of good things in it. See what happens when you write one sentence and other short versions. See what happens when you turn all the visuals into art notes so the pictures and words do different jobs and support eachother.
(I would recommend Invisible Ink by Brian McDonald if you are serious about story telling. it is a to-the-point tool box for building great stories of every kind. Pixar uses this book. I finally read it after listening to his podcast "you are a story teller" and it is just so great--like a HTFYStory class 
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