What is the quiver attached to, looks like it's just hanging in midair behind her.
Depending on the light source location (I'm assuming top right), there should be shading on the undersides/ bottom left of most things. Notice what shading you had under the shirt/ onto the skirt? You didn't do the same thing from the skirt onto the pants, though you should have.
Proper posture for firing an arrow:
-Left hand closed around the bow, arrow resting on top
-Left arm straight out, usually in the desired starting angle for the arrow
-Right hand: two or three fingers holding the bowstring back, with the arrow nocked in between the index and middle finger
-Right forearm should be above the backarm (?) at an angle, with the right hand close to the cheek
-Eyes forward and locked on target
-Legs split, but mostly perpendicular to the ground
-Left leg should be
behind the right one and forward more
Here's a pic for clarification:

Here's another:

Hope this helps :D