Coetzee's story, set on a Afrikaner Boer farm in South Africa, reports things out of chronological sequence and thus may seem hard to follow, making it harder still to identify fact from Magda's fantasy.
In section 123, Magda, the narrator, has just entered her father's room in bright morning light and found her father sitting on the floor unclothed except for the green curtain he has pulled down, rod and all, to drape himself with. Hand to her mouth in horror, Magda notices his face is yellow as their eyes lock and she puzzles to discover the expression on his face.
It is now that the section you ask about occurs. In section 124, Magda, without explanation and equally without any immediate clue to chronological continuity (chronology: cause-effect logical progress of time through trackable events), goes about the interior of the house closing doors in a small inventory of their house "shaped by destiny like an H" that signifies a Cape Dutch Gable house. In section 125, a short section of one single sentence, she notes that the cups (a recurring motif) have not been washed.
It is a puzzle as to how to understand these passages. Is she stepping out of chronology again? Is she suggesting that in the face of the catastrophe facing her, with "flies in her father's room," she honestly walked deliberately away and deliberately closed doors all throughout the H shaped house? Either way, a sense of Magda's psychological profile is represented.
These passages tell us that Magda is detached in some significant ways from reality and that she behaves, at least at times, on psychological levels that are rather automaton like (automaton: a machine that imitates human movement and action and seemingly has independent volition though only a machine). This characterisation of Magda can be important in understanding her as the tales she tells become more and more macabre.
I am running now as I have not run since childhood, fists clenched, arms pumping, legs toiling through the grey sand of the riverbed.... a hundred-pound animal hurling itself through space under the impulse of disaster.