Part of that flat look might be because of the tilt of her face towards the viewer...so that the plane of the forehead and the two under her eyes all appear flat due to a lack of value changes. On her right side (left side of the picture plane) you have a light area above the upper lip that works well. Perhaps leave the plane under that eye and darken the plane under the other eye. That's one idea anyway. She looks great as always!
You are amazing with water colour =o!!! I love how you were able to make her lips look so glossy compared to the rest of her skin. Knowing me, i'd probably make it look as matte as her skin on accident xD but yeah.. what i was trying to say was great job!