I would turn down the lights on the stairs, so to speak. Paint her as if the only light is on her and then put the lesser architectural elements in the dark and paint just enough of them so a viewer can still tell what it is. The dark banister will fade back if the area of the stairs is dark. Also the area of the floor behind her could be made much darker and maybe even show her shadow across the floor and then up the wall, which will give the painting more depth. Turn down the light on most of the chair to play it down and also make the strange perspective caused by the camera lens less noticeable.
Think chiaroscuro, the technique of using light and shade in pictorial representation, the arrangement of light and dark elements in a pictorial work of art. It is Italian, "chiaro" meaningg bright-light, and "obscure" meaning dark or no light.) The word is also used to describe a method of painting in which you paint the lights and darks in a brown or greenish toned under painting. It is called this because you paint lights and darks only with that layer of paint.
Think chiaroscuro every time you think composition. The placement of your lights and darks is as important if not more important than how the objects are arranged. I feel it is more important because if you place an object in the dark, it is hidden from view and the light and dark shapes formed by the shadows and lights are what give the painting form and direct the eye to points of interest. (Color, edges and line also do this so I don't mean to say that the lights and darks are the only thing to worry about.)
I always try and take a tip from Caravaggio on composition -- put your subject in the spot light and the supporting cast in the ambient light and the unimportant in the shadow.
For Caravaggio, chiaroscuro meant that god was in the light and the absence of light was the absence of god. And he used this technique extremely well. In the painting below:
You can see more of his work here:
http://www.artrenewal.org/asp/database/art.asp?aid=589
P.S. You do not need to go as dark as Caravaggio with the darks but you need some more darks to contrast with the lights.