Million dollar question is if she was extending the wrist pre surgery.
If yes then definitely exploration urgently. Can wait for a day or 2 to see if any hint of recovery is there fasciculations etc.
If she was unable to extend even prior to surgery, then you need to wait as usual for nerve recovery 6-9 months.
Next Steps
Consult online.
Health Tips
Pressure (compartment syndrome) building around nerve or nerve getting entrapped... as told by surgeon. both are medical emergencies...
These should be clinically evaluated and explored at the earliest. There is no wait and watch for this.