Margot's strength is in her sensitivity and her ability to be true to herself. She remembers  a better world on earth, where the sun often shone, and is strong in her dislike of Venus, where the sun only comes out once every seven years. She shows integrity in her loyalty to earth.

She reveals her artistic sensitivity when she writes a poem about the sun: "I think the sun is a flower, / That blooms for just one hour." One of the boys in the class protests that she couldn't have written that. 

Because she is true to herself, she tries to communicate her memories of the sun to the other children, comparing it to a fire in the stove and a penny. Because she is nonconformist, she won't join the other children in their games. She doesn't pretend to like things she doesn't like.

As with most people, her strengths are also her weaknesses. Her integrity--being true to herself--includes a lack of social skills: she doesn't seem to realize how much she is alienating the other children and acting as if she is superior for having seen the sun. Even though she was true to herself in rejecting Mars, she might have made some attempt to relate better to the other children, though her depression might have made that impossible.

Her sensitivity is also a weakness: it means she writes nice poetry and has vivid and poetic memories of the sun, but it also leads her to scream and not want to take a shower. It causes her parents to think of leaving Venus early, despite the money they would lose.