The correct answer is A. Watchful waiting.
Kybella (deoxycholic acid) is an FDA-approved treatment for injection into the submental area. Cases of marginal mandibular nerve injury manifesting as an asymmetric smile or facial muscle weakness were reported in 4% of subjects in clinical trials. All cases resolved spontaneously within a median of 44 days. It should not be injected into, or in close proximity to, the marginal mandibular branch of the facial nerve.
Given the results of the clinical trials for deoxycholic acid, the best initial step in management is watchful waiting and close monitoring of the patient. If the patient does not improve in the next 1-2 months, additional investigations can be considered. In the trials, all cases of marginal mandibular nerve injury resolved spontaneously within a median of 44 days.