Use the hose bib Jerome suggested along with an electric water valve. Run the hose out to the building along with wires for a switch to turn the water on and off through some four inch PVC or other conduit. Wire in a warning light by the door that comes on when the water is on. She turns the water on when she gets there and off when she leaves prompted by the warning light. Once the water is off she can then open the valve at the building to drain the hose into a container to use without waste.
Dan