Saft sits up and faces her window as if she knows where she needs to head out now, though she doesn't want to disturb Rider nor does she want him to accompany her even if he insists upon doing so. She knows how protective he is of her and if he knew what thoughts she had been conjuring up in her head about possibly going to speak to Caster on her own, then he'd definitely want to be there besides her or even attempt to talk her out of such a suicidal idea.

However the grail doesn't take nap breaks and nor will the remaining servants. She needs to be up, dressed and prepared to face the coming storm. There's no need to disturb Rider just yet.