Sentence 1: Jessica was trying to chat with her boyfriend on the phone. 
 Sentence 3: Quietly, she got up and walked to the door 
 Sentence 4:  Then, she quickly opened it and kicked her sister 
 Sentence 5:  The two had a huge fight then, but luckily mom took Jessica's side 
 Option 1: He could tell his little sister was spying through the door. 
 Option 2: She could tell her little sister was spying through the door.