It will take her 0.5 miles / 3 mph * (60 minutes / 1 hour) = <<0.5/3*60=10>>10 minutes to run half a mile.
It will take her 0.5 miles / 1 mph * (60 minutes / 1 hour) = <<0.5/1*60=30>>30 minutes to walk half a mile.
Her total time is 10 + 30 = <<10+30=40>>40 minutes.
#### 40