The paragraph that would help build tension if added to the story is:
"As she struggled to free herself, the bus pulled into view. She waved her arms wildly, but the driver didn’t notice her. And she was still stuck. What was she going to do? She could not be late to school today."
This paragraph heightens the urgency of Sylvia's situation, emphasizing her struggle and the immediacy of the bus arriving without her being able to get free, which builds tension in the narrative.