If you want to create a portrait with highlights and shadows, you've got to get AWAY from the light source. Highlights and shadows are a good thing in portraits! They give your portraits depth and dimension. Without highlights and shadows, your subject looks flat. No one likes to look flat.
Think about it. If you are next to the light, you will NOT be able to see the shadows. The shadows will be on the OTHER SIDE of your subject. So, if you're shooting the front of her face, the shadows will be on the back of her head. Not useful. Unless you're a weirdo.
The ONLY way to see shadows is to get AWAY from the light. As you do, you're now in a position to see those important shadows. This is true whether you're using a lamp, window or open sky.
Obviously, this is true with flash. On-camera flashes have a severe disadvantage when the flash is pointed directly at your subject. The problem is that, since the light is by the camera, the shadows are on the BACKSIDE of your subject. No one wants that weirdo.
It's usually better to use an OFF-camera flash (OCF) with a transmitter. With an OCF, you're able to position the flash away from you and see highlights and shadows. If you don't have an OCF with a transmitter, point your flash towards a wall so that the light that is striking your subject from a different direction than where you're standing - making you able to see highlights and shadows.
Creating highlights and shadows is one of the ways you can make your portraits look professional. Of course, you can learn all of the ways at www.fotomethod.com.