I'm not quite sold on the posing and framing of the above shot...her placement within the frame area is a bit far to the right for the eye direction she has, but she's so, so beautiful! I took your original shot and cropped it a bit, and converted it to a couple similar yet subtly different black and white versions.
Kind of going for an old, 1940's-era feel and look. Part of the 1940's-era look was the use of 4x5 inch film cameras and shallow DOF...your 50mm at f/1.8 shot gives a similar shallow DOF look...and the way the corners of the frame are somehwat blurry, and the DOF that fades fast, from the sharp lips to the OOF ears...those things are sort of 1940's0-style image characteristics.
For some reason, she and this second, more-contrasty B&W look remind me of an old photo that I think I have rattling around in my brain, at a subconscious level. To me, the best things about this ARE the high-sun caused eyelash shadows, her full and perfectly-shaped lips, and the sideways-directed line of gaze that she has.And that lip-shadow on her chin--sublime! The arms behind head, beginning model type pose was not ideal, so, I cropped that out, and tried to focus on the facial shape and the way the light reveals the dimensions of her cheeks, lips, and so on.