I would imagine she has all 3- black, white, and bare copper. However, the black is probably the power coming in, the white is the switched leg going back to the fixture. Both hot. Copper would be the ground. I see a lot of older houses with lights wired that way- the power feed goes directly to the fixture box, then sent to the switch box and back over one Romex cable.
If wired by a electrician the white will be your feed/hot wire and black will be the switch leg/load.