A 6-Year-Old Male Is Brought to His Pediatrician's Office with Chickenpox

A 6-year-old male is brought to his pediatrician's office with chickenpox. He has had symptoms for one week, and his mother is concerned about the patient's 8-year-old sister because she had a long, painful chickenpox infection 2 years prior. Of note, the patient was not vaccinated against chickenpox because his parents did not think it was a serious enough virus to warrant the pain of the injection.
-When the patient's mother expresses concern about his sister being reinfected with chickenpox,what is the most appropriate response?  

A) Your concerns are valid,but his sister developed an active natural immunity to chickenpox because she has already been infected.
B) Your concerns are valid and there is a high likelihood that his sister will become infected again.We should probably administer the vaccine.
C) Your concerns are valid and there is no way to protect his sister from becoming reinfected except to keep her at least 15 feet from your son at all times.
D) Your concerns are valid and if his sister is reinfected,her symptoms will be less severe than her initial chickenpox infection.