Celestia's Dawn, how beautiful it is, as we watch the beautiful pony rise the Summer sun, she looks down and smiles at her pony subjects, such a kind ruler and her beauty comes with her every dawn.
The birds wake up with Her dawn, as they spread their wings for the first time since Her Sister's night, she wakes them up with her sun's gentle kiss of its rays, they tweet their pretty songs and soar through the skies as the Pegasus ponies get ready to make the day's weather.
The fish wake up with the dawn, warmed up by Her suns warmth and they frisk around searching for food, their bodies fully awake now hoping not to be eaten by any wandering bears or cats.
The ponies of Equestria wake up and stretch to get ready for the day, the Pegasus ponies wash their wings and the Unicorn ponies practice their many skills, and the Earth ponies make breakfast for their families and get ready for the new Day.
Everypony from any race can enjoy Celestia's Dawn, the warm reds, the orange hues made from the sun, and the yellow glow Her sun makes, is simply beautiful and cannot be copied by anypony, no matter how hard the Unicorns of old tried, they could not make The Dawn as bright and beautiful as Celestia, and therefore she gained her cuite mark, a shimmering sun.
Okay, so you might want to work on punctuation. Also you have an extra space in the very first line. And you capitalized Her every time, which I get if she's divine but you aren't consistent with Her and she.
This is just me, but I try to vary my language up enough so I never use the same adjective or verb in a single paragraph, barring essential building-block words.
sun's
Maybe try to vary your language a bit more too.