"All Summer in a Day" imagines a Venus whose weather is one of almost never-ending rain, where the sun comes out for only a brief span, during one day every seven years.

Margot herself had come to Venus five years earlier, so unlike the other students in her class, she actually has memories of sunlight, thanks to her time on Earth.

The key to understanding this question is to recognize that Margot does not want to live on Venus. She is profoundly homesick and wants to return to Earth. This brings us to the image of her reaction to the shower, which is closely tied into her suffering on Venus. What defines life on Venus is its incessant rain, to such a degree that it blots out the sun, and this is one of the factors which, for Margot, makes life so miserable. Her reaction in this scene amounts to a rejection of her life on Venus, pointing back to her profound desire to return to Earth.

Unlike the other children in her class, Margot was born on Earth and can vividly remember what the sun looked and felt like before she traveled with her parents to Venus, where it constantly rains all day for seven consecutive years. Margot desperately wishes to return to Earth, where she can enjoy the sunlight, and has become increasingly despondent on the rainy planet. Margot absolutely detests the rain and even refuses to take a shower at school. Margot's refusal to take a shower symbolically represents her negative feelings regarding the rainy planet. The water from the shower reminds Margot of her gloomy, depressing environment and negatively affects her anxiety, to the point that she begins to scream when she comes close to taking a shower. Her refusal to take a shower also reveals her desire to travel back to Earth, where she can finally experience the sun again.

In Bradbury's story, Margot is the only child her age on Venus who consciously remembers sunlight. The other children of her age group came to Venus when they were so young that all they remember is the constant rainfall that continues for years and years on end. To them, all this water is normal. Margot, however, remembering sunshine, finds the rain depressing, to the point that her parents are considering returning to Earth because of her despondent state. The shower only serves to remind Margot of the endless rain, which she is thoroughly tired of. She wants to be dry, not wet, baking in the sun, not under the tyranny of a constant downpour, and so rebels against the shower. To her, the shower symbolizes the constant rain she hates.