It appears to me that you took time to put her in shadow, away from the harsh daylight, and used fill flash to compensate. From the catchlights and the shadows, it appears that you're using an on-camera flash. You may want to explore putting your flash on a bracket, which would make it slightly more "off-camera" and will make the light more dimensional (ie, less flat and more shadows). The on-camera flash also put hot spots on her lips, which to my eye diminish the quality of the image. The f/4.5 still has too much DOF in that the background is rather distinct. Alternatively, instead of using a shallow DOF, maybe choosing a less cluttered background would help.