First of all let me suggest you shoot with this model as often as possible. She has a great figure and seems very expressive.
I think the big issue with this image (for me at least) is the lighting. I know you do not have pro strobes available, but there are things that can be done to improve the look with a on camera strobe. Move her away from the background, difuse the strobe with a white sock, open up the Fstop, use a tripod, find more available light (through a window)
Just keep playing with light and camera settings and keep photographing that girl.
model credit: Leigh Ann (Dallas TX)...shot with only available light, reflected with a piece of white foamcore