Though its very hard to diagnose with just a picture, But this could be a spider bite, see... there seems to be 2 puncture marks ( Fang Marks) on the lesion ( which may be seen in some spider bites too like u mentioned..). Does she have any symptoms like fever, headacne, joint pain and other if any. My suggestion would be to consult a doctor immediately. Your doctor will carefully see the lesion, do some blood and urine tests and rule out if its a spider bite and prescribe some oral and topical antibiotics to prevent further infection or other measures accordingly.
Being said that there are some other dermatological condition that might resemble but your initial step is to seek emergency help. Though severe complications are rare in spider bites, but is important for emergency visit. Besides some rare systemic complications of spider bite, the skin around the bite might get necrosed and leave permanent scar on forehead. Forget the dermatologist for now if he/she has long waiting list and visit nearby emergency clinic.