Really nice Az, - you are improving.
First, the model is beautiful, and you have achieved good eye contact.
I have a few comments and suggestions.
Looks like a window behind her, so you had access to natural light, and you had access to a good background using what look like brown drapes? And you didnt use either! I know you were focused on the subject, but its also important to consider the setting, and the light. Good natural light will always look better for a portrait when available.
If you had still used the lights and positioned her in front of the solid colour background, you would have eliminated a cluttered look.
The aperture selection is vital in a portrait. Youve used exactly the right focal length, but an aperture of f/5.6 is the sweet spot for most lenses, with f/8 almost as good, but giving more dof.
Use aperture priority, and set it to 5.6 or 8. The ensure you are selecting to focus point in the viewfinder that aligns with the closest eye for the best results.
Theres a little too much light on the shoulder as you mention, and you can only control light using a snoot to prevent the light from spreading, - or again better to use the window light. Also, moving her hair away from her near eye would have looked better.
It doesnt look right in the histogram when I look at it in Photoshop, and I can see quite a bit of spillover on the right side, meaning blown highlights, - BUT its just a little. The problem really is that the bright area appears close to, and in front of the face and tends to distract.
The use of the diffuser may not have been needed, and bouncing the flash off the ceiling is effectively using the ceiling as a diffuser, and putting one on the flash reduced the amount of light reaching the ceiling.
Anyway its quite good. I did load a mod cropped to place her eye on a third; then added white catch lights to the eyes, while removing what appears to be a second highlight lower in the eye ( the result of two lights perhaps), sharpened the eyes a little.
Hope all this is helpful, and keep working with this mode!