A 30-year-old woman comes to the office for evaluation of an asymmetric smile. Two months ago, she underwent primary neurorrhaphy of a facial nerve laceration 2 cm lateral to the oral commissure. Physical examination shows no elevation of the upper lip with smiling on the side of the injury. Which of the following is the most appropriate management?
A) Cross-facial nerve grafting
B) Facial sling suspension
C) Free muscle transfer
D) Injection of botulinum toxin type A
E) Observation