。
She was idly flipping through the pages of a magazine.
Literal
She [topic-は] absently magazine's pages [object-を] was-turning.
めくる is a tactile verb specifically for turning pages, peeling something back, or flipping through — distinct from 開く ('open'). The combination with ぼんやりと paints the action as half-engaged: she's physically turning pages but not really reading them. The と adverbial form on ぼんやり is the slightly more deliberate variant of bare ぼんやり.