pretty underexposed. no detail in the hair at all. needed some fill flash. is this cropped at all? lot of extra space up top.
blown up it looks like there might be some soft focus on the face, but its so dark its hard to tell.
i like the background choice though. if you had used a little diffused fill flash here it really would have looked nice.
Pretty much all of the above. I would add that given the light on top of the head, in absence of a flash for fill anything white will act as a reflector to move light into her face. White poster board a sheet, one member on here even used a newspaper with excellent results.
In photography, light IS the photo...without good light you can't have a good photo. I would suggest either doing something creative by lighting her face with the blue ambient light from behind, or add light (flash).
Does your camera have a built-in flash? If so, then perhaps you can adjust the power output of that to be a small amount, something photographers call "fill flash". I see that your metering mode was set to "pattern", which averaged the entire scene, including the lights, making your subject's face underexposed.
Anyway, here is a slightly different crop that you might consider: