Becky is not a well-developed character. Instead she is the symbol of the beautiful, unapproachable girl--"a lovely little blue-eyed creature with yellow hair plaited into two long tails, white summer frock and embroidered pantalettes." Her striking looks capture Tom immediately. Yet even though she is not a fully developed character, her influence on Tom Sawyer is immense, and it is this outward effect on Tom that is important. Tom's attraction to Becky is one of the charms of the novel. It is the typical case of puppy love and infatuation. It exposes the more mature side of Tom's character.
Becky is very pretty, proud, and jealous, and she seems to appreciate Tom's devotion only after he allows himself to be punished in her stead. When she and Tom are lost in the cave, however, we see that she is not strictly a static character, that is one who never changes. To the contrary, Becky is indeed worthy of the affections that Tom showers on her. Although fearful of death in the cave, she fully trusts Tom and does not blame him for their terrible predicament. She actually shows more courage and stamina than the reader would have expected under the circumstances as she faces death with a serene bravery.