The red veil conceals the face; its removal reveals brightness. The paired images of twilight and moon express that opposition in poetic form.
«فَزَحْزَحَتْ شَفَقًا»
She shifted a red twilight aside.
Zaḥzaḥat suggests moving something away. The plain description “she removed her veil” would tell the event, but “she moved twilight away” sets the same action against the vast scene of an evening sky. The verse gains force through this imaginative expansion.