Rowena needs a spell from the book to break the magical "binding" placed on her by the Grand Coven, allowing her to regain her full power and protect herself from Lucifer.
Just as the witches escape, makes her reappearance. Having survived her latest death at the hands of Lucifer, she tracks the Grimoire to the bunker. [S13E12] Bad Moon on the Rise
One of the most praised segments of the episode is the heart-to-heart between while they wait for Dean in Oklahoma. Rowena needs a spell from the book to