Good, but you ouverlooked a few things...
Subject: Pose is awkward - she's standing almost too straight. The rifle doesn't seem to shift her weight at all; how would one hold a weapon that size and weight, at that angle, with only one hand and not bend the wrist? The right arm seems to be forcing in a straight position behind the leg; a slight angle in the elbow would fix that. Legs appear to be locked straight as well, "twinning" the pose; again, how she holds that rifle up with her legs creating that center of balance is beyond me. Wonderfully detailed, but defies the laws of physics.
Background: Seems to have been rushed, but it does relay the dark atmosphere of the environment, which can be difficult to do. The ambient lighting is mostly correct,save for a couple reflections off the rifle where there shouldn't be any. The creature silhouetted against the flames is a nice touch, as is the dead one behind her.
Summary: This is four years old, and you've probably improved since then. But in spite of your attention to detail, there are definite points where this could have been done better. 6/10 and 3/5 from me.