Nice work on the portrait. Some things that I notice are:

The wrap around her body appears sharper than her eyes - suggesting that the focal point was set in front of her. With portraits, you want to make sure that you nail the focus on the eyes.

Learn the limits of your gear - I have no experience with your particular lens but the range, 18 - 140, is suggestive of a lens that has made some major compromises for that zoom-ability - including compromises in sharpness. Even given this, it's likely that between a certain range and aperture, it'll have a "sweet spot." Do some experimenting to find the sweet spot and use it to your advantage.

Sharp Photos and Soft Skin are, generally, opposites - Most skin softening is done with make-up and/or with post processing work to smooth out the skin. I wouldn't work for getting soft skin out of camera - rather, go for tack-sharp eyes.

Compose for non-distracting backgrounds and leading lines - The blown out section on the left doesn't add to the photo. However, the building on the right has a pleasing color and leading lines to the subject. I'm wondering if you could have aimed from more to the left so that the subject blocked that building's doors while expanding the wall color to take up the entire background near the top.

Overall Lighting Quality - She's being back-lit but there's enough light bouncing around inside that it's actually a very well lit portrait, IMO. I'd personally dodge the face a bit to brighten it up in post, but otherwise think this looks good. If you did want to light it differently, you have many options. A speedlight could be used to bounce light from an interior wall, or reflectors could be used to redirect even more of that outside light onto her. If you wanted to flatten out the lighting, you could use a scrim to soften the incoming light and then use the speedlight/reflectors to more directly control the lighting.

On shooting Auto - In general, don't. Once you learn exposure, you'll want to control everything (shoot M) or set a priority to let the camera do the rest (Av or Tv). For portraits, blurred background help to isolate the subject - so in general, you'll want to set the aperture. At the very least, control this and shoot Av and set your ISO yourself. See what shutter speed the camera is computing and make sure it's in an acceptable range - (1/focal length for handheld shots, for example). Adjust Av or ISO accordingly until the set shutter speed is in a good place.

Cheers,