Due to a viral infection, the patient was unable to move the muscles on the right side of her face. Hence, her Facial nerve or Cranial nerve (VII) is impaired. This cranial nerve is in charge of controlling a person's facial expression muscles as well as the release of saliva and tears. If that particular nerve is injured, it causes weakness on one side of the face, and loss of sensory and sensation is also experienced.
References:
Tortora, G. J., & Derrickson, B. H. (2018). Principles of anatomy and physiology. John Wiley & Sons.
What to Know About Cranial Nerve 7 (Facial Nerve). (2022, May 24). Verywell Health. Retrieved October 6, 2022, from https://www.verywellhealth.com/cranial-nerve-7-5270869