Oh it’s completely different. Of those three characters the only one that’s recognisably the same as the book counterpart is Lasher, but even then he’s toned down quite a bit and the novel plays up his ethereal nature as a spirit.
With Rowan, to put into perspective, she’s much more stoic and quietly confident and Rice stresses that there’s more of an androgynous aspect to her character. If you were to go for book accuracy, you wouldn’t cast Alexandra Daddario, you’d cast Emma D’arcy.
There’s this huge chunk of the novel that’s devoted to Rowan’s romance with Michael (Ciprien’s book counterpart whom they largely cut out and amalgamated with another character) and the two of them creating a life together. They get married, Rowan is expecting a child etc…Lasher kind of exists as this horrible seductive interloper whom is sort of stealing Rowan away from that life, even as she thinks she can control him. By the end of the novel Lasher has taken Michael’s wife and child from him, and it’s an absolutely horrific and tragic note to leave the book on.
The show comparatively …well, they went for something more toothless and tried to turn it into an empowering moment for Rowan.