There will be people like her who will always belong to the sky, because you know that her rightful place is among the stars, and the galaxies, because you are sure that she is above earthly things.
That's why no matter how hard you try, she will never be yours, not fully, because she might be with you, but her eyes will twinkle and you know she's gone, she's in a place that you cannot reach.
So it's okay to let her go, because you know that deep down, she was never yours to begin with. She's just a traveller from another universe.