"Dosage adjustment with strong CYP3A4 inducers: 50 mg once daily when used with potent inducers (eg, rifampin, phenytoin)".Since the dose of 50 mg can be given safely, you needn't do anything but be careful it doesn't happen again. She should take her regular dose at its next scheduled time.

No reason for panic. Exemestane is an anti-estrogen drug that of course can cause trouble if you swallow a whole handful, but one extre as a one off event witl not cause trouble.