I have no expreince in this but I'll jsut fire off what I feel. She looks like she is gonna fall off the chair and her feet are in an awkward position for me. Also they way her wrists are bent makes it look like it got broken. You can try asking her to tilt her body slight more away to the camera and have her tilt her head slight and lean it towards the camera instead. As for the hands and feet I'm not too sure also.
her posture makes her look uncomfortable in the chair. as pointed out by raptor84 her hands make her look tensed. while posing hands, from what i learnt from photographers i worked with, you need to direct her so that she does not put any strength in holding her hands' postures.
the greyish background and Victorian chair give a rather serious setting, not quite complementary to the more casual expression and outfit intended. of course it doesn't mean that you can't be playful in serious setting, but as a rather simple depiction of a person's portrait it does not fit together to make a complete picture. there's abit of distortion in bodily proportion probably due to a wider angle used, a little more distance between you and the model and using a longer focal length might help correct it.
but i second that she's in a quite un comfy position. Personal preferences, if she can be positioned more towards the left side of the image, giving more space on the right... hm.. i think composition better. hm.. mayb she can sit normaly, cross-legged and crack her a joke n when she breaks the smile, BAM! the shutter goes too. Her smile ... seems stiff. over all the lighting not bad.