The volunteer walks 1 mile to the dog shelter and another 1 mile back home, so she walks 1 + 1 = 2 miles each day.
She walks 4 dogs for 1/2 mile each, so she walks 4 x 1/2 = 2 miles with the dogs each day.
Therefore, she walks a total of 2 + 2 = 4 miles each day.
Over the course of 3 days, she walks a total of 4 x 3 = 12 miles.
So, the volunteer walks 12 miles in all.
