I would probably have had her pose standing up, which is usually a much easier way for people to pose. Seated poses like this are tricky, and the best way to do them is to have the person seated on the very front edge of a rather high stool or posing box, or a tall bench, so that the feet just barely touch the floor, and with the person sitting up really tall and straight, then leaned forward from the waist, with their head out in front of the belt-buckle, and the camera placed a bit above eye level. She is sitting too "casually" for this to make a really great seated pose. What looks best in a seated, posed photo like this is very different from the way a person would sit in normal, everyday situations.
I can see this is a direct, on-camera flash shot, which leaves the tell-tale flash shadow around the person. Not sure if you have a hotshoe-style flash unit, but if you DO have one, I would try having her stand near a white wall, and aim the flash off to the side, so it hits the wall. Have her turn her body away from the wall, and then her head turned back toward where the light is bouncing off of the wall, Shoulders angled around 30 degrees to the lens, and the shoulders as I said going "one direction" and the head "looking the other direction".
Another tip is to bounce the flash BACKWARD, off of a wall, and a bit of the ceiling, so the light bounces forward AND also rains down a bit.
Cheap backgrounds: I like the Target store's microfiber "plush" blankets. Dark gray, white, brown.
Room Essentials® Microfleece Blanket : Target
and this specific type is good too.
Threshold? Microplush Blanket : Target