I think that Susan's lack of affect represents the extent to which she is responsible for the conflict she faces in "To Room Nineteen."
Susan does not actively seek out the conflict she faces. However, she fails to cultivate an emotional frame of reference in assessing her life and her marriage. Like her husband, she steeps everything in a cerebral paradigm. Susan does "everything right, appropriate." She acts with an excessive desire to represent a "balanced and sensible" approach. Lessing writes that such an approach demanded that Susan and Matthew use "their intelligence" as a way to offset a "painful and explosive world." Susan lacks an inner dimension to understand this part of existence. When she faces challenges that necessitate leading with the heart, she embraces an almost- academic approach: "People like themselves, fed on a hundred books (psychological, anthropological, sociological) could scarcely be unprepared for the dry, controlled wistfulness which is the distinguishing mark of the intelligent marriage." Her emotional inabilities result in a life akin to a "snake biting its tail."
It's difficult to blame someone for not being feeling enough. However, Lessing's story demonstrates the necessity for emotions. Susan's flight to Room Nineteen and her experiences with its solitude reflects this. However, part of the reason she experiences challenges is because of her inability to stop the intellectual roller coaster of her life. She has to accept some responsibility for a lack of emotional balance. Intelligence and "sensible" choices are essential. However, they only go so far and an inward and reflective capacity is needed. It might be uncomfortable, but as Susan demonstrates, it is better than the alternative of living life without it.