I opened up one shot in Photoshop and checked the R-G-B histograms individually, and all showed under exposure. I quickly added exposure and + 1.4 stops looked almost perfect to me. If the main light flash is at 1/8 power, I'd feel free to power it up a bit higher and maintain the same f/stop, since judging by the histogram your exposure is about 1.4 to 1.5 stops under maximum allowable before things start to clip on the highlight end. I would try hair light at 1/8 power and main light at 1/4 power as a start,which would be the same relationship you have now, only with a stronger main light output.
Keeping the flash four to five feet away with a smaller to medium-sized umbrella is about right; as you can see, at that distance with that particular umbrella, it gives a moderately hard shadow on the nose. To get the catchlights higher up you might have to put the umbrella so the top is actually touching the ceiling, or lower the posing stool or bench.
Let's take shot 2 as a basis:Have her sit up very tall,and lean forward ever so slightly from the waist. Tummy in, shoulders back, chest out, good posture,spine straight. I would angle her shoulders more steeply toward the camera, and lower the camera at least six inches; this will pull her far shoulder around and more out of view, and will bring her bustline into view and will be very flattering overall. Turn the camera to a vertical orientation,and her body will be filling up the width of the bottom of the frame, creating a "base" for the portrait,without the excessive dead space on a horizontal framing. Trust me...a little tiny of refinement in the posing and framing departments will elevate #2 to a real portrait shot.