Headace and it feels that her one side of her head is swollen?

Migraine?: A common cause of one sided headache is migraine syndrome, which can also cause a sense of fullness on one side of the head. There are many other possible causes. If headaches are a significant concern, please see your doctor for evaluation.

Nonspecific: Headaches can be due to tension,muscle contraction, migraine, intracranial problems like hemorrhage or growths, inflammation of temporal artery or infection. More description of the headache is needed. If the headache is very severe or accompanied by neurological symptoms or vomiting or fever or stiff neck, go to the emergency room. Otherwise take Tylenol and observe for other symptoms.

Headaches: Can be less serious such as migraine or secondary to viral illness or could indicate more serious problems. Difficult without further information to say. Would neeed a doctor examination for specifics. Here is general info re causes of headaches and when to seek urgent attention. https://patient.info/health/headache-leaflet