Why does the author include the scene with the dust storm

I think the natural occurring element of the dust storm adds another layer of conflict and stress in the story. A month after the dust storm, Esperanza notices that Mama looks pale and encourages her to lie down. Her mother, tired and worn down, breaks out into a fever. A young doctor explains that Mama has contracted Valley Fever, a condition that results from dust spores growing in the lungs. Esperanza is rocked by the news that Mama will take six months to recover - and she may not even live that long.