The placement of the thighs looks really unnatural. They're incredibly short in this image. It's okay when she's leaning, but as soon as she sits up straight it looks more like she's on a stool than on a chair. Her back also feels really upright and stiff for sitting.
I might also add some little "exclamation" lines to make it a bit more dramatic, as I'm assuming this will probably be done for humor value.