This is a basic low-key shot, but without the benefit of a flash you're going to need to work harder to get the big difference between subject and background.

Without a flash, a good bet for the kind of shot you're talking about is to pick an exterior doorway where whatever's outside will be good and dark, like a backyard with no lights. Open the door wide and ask the subject to stand just outside the door, so that light from the room falls on her face and on the violin, and the background behind her is good and dark. You can shoot from inside the house if you want her to be fully lit, or you can try to stand outside with her so that she's lit from the side. The key, again, is that whatever's behind her should be much darker than the light on her face and violin.

You want to set the camera so that it'll give a good exposure for her face, and at the same time really underexpose the background. If there's not enough light to do that, bring more light to the party. Get your three favorite cousins to stand inside the house and hold table lamps, work lights, whatever you've got available, near the doorway. Adjust the brightness by having them move closer or farther away. As long as you've got a big enough difference in brightness between subject and background, the background will go black.