I would have loved to see this framed as a "tall". You positioned the umbrella in a pretty good spot to give nice catchlights in the eyes. Clicking on it and seeing the D750's gorgeous image quality is pretty impressive....what an amazing imager that sensor is! There was a time when one could only dream about showing that much detail with so little grain, or noise!
I think the thing the landscape orientation hurts the most is in not showing her clothing or her womanliness...this is just an unusual place to cut off the torso and yet to include so much background. You have that nice, summery, light-bright-airy background, which is a good thing. Her head just touches the right-side tree in the backdrop, in a slightly unsettling way that could be considered a figure/ground attachment flaw....or is it a deliberate testing of the figure/ground rules?! We can see some flowers in the lower left quadrant, and the two big trees in the center of the frame, and sort of a white bench that appears at the side of her head
I like her slightly cocky, yet slightly enigmatic facial expression, and her eye contact with the lens is really good. If there's a nit, it's that one nostril appears big, the other one, almost totally invisible...I wish her head had been turned a bit more toward the camera, so the missing nostril would have come in to bring more symmetry to the shot. You appear to have totally NAILED the focus placement and DOF on this shot.
What I see is good focus, good lighting, an attractive Pixie-like woman, presented with a lot of 3-D POP! in front of a very defocused background...I just wish more of "her" was shown...the cut-off above the armpit is not quite closing the circle for me. I think, as a horizontally-framed shot, there needed to be more of "her" shown, a bit lower down, maybe from four or five steps back farther away, OR the camera rotated to a "tall" orientation, to get more of her, perhaps down to about the elbow region, as opposed to above the armpit as where the body is cut off. I totally "get" the way this has been umbrella lighted, superbly focused, and the DOF band expertly placed...I just thing it needs more "woman" to be shown and contrasted against the lovely, airy, defocused backdrop. I get the idea here--Her, shown against Location. You have even lighted her with umbrella lighting to make the light levels look well-matched, but my eye craves seeing more Her to go with the background's percentage of total frame area.