The weather on Venus disagrees with Margot so much that her parents are thinking of returning to Earth. This seems "vital" to Margot, though it means the loss of "thousands of dollars to her family." Margot seems less able to adapt to the climate than the other children. One day, she freaks out in the shower, putting her hands over her ears and screaming that the water can't touch her head.
The weather seems to have made Margot depressed. She stays apart and doesn't play with the other children as they run through the underground tunnels. She won't sing their songs about happiness and life. The only songs she will sing are those about the sun and summer. Unlike the other children, Margot has memories of Earth and the sunshine, so she has a point of comparison. This knowledge causes her to feel deeply alienated from the weather on her new home.