Almost everyone is infected but he time they reach adulthood but most people don't have clinical infections where you have actual fever blisters/cold sores.

The stress of the surgery likely allowed the virus to replicate to a level of producing a clinical reaction. Quite painful and very annoying. A doctor can prescribe some valacyclovir (antivirals) but their utility after 2 days of skin infection is debatable.. because she just had surgery, probably a good idea to get some if you can. You can also use Abreva OTC, but that decreases infection duration by like 12 hours if you start it immediately when the infection starts.

Keep the infection site clean, try to avoid touching it and spreading the virus.