It's mean to wish death upon someone.
Becky gets into fights with her mother about Becky's unconventional clothing style.
Becky wants her mother to understand how stifled she feels.
Becky resolves to calmly discuss what her choice of clothing means with her mother.
During a fight Becky angrily tells her mother to drop dead if she can't accept her self-expression.
Becky is better able to get her feelings across to her mother, and they are able to reach a compromise.
Becky is remorseful because her words make her mother cry.