It might help us if you could describe the highlight a little more. Is it a glow, a border, something else? There are probably several ways to accomplish this.
You could create the halo in DRAW or Photo Paint. In both application the image should have transparent background.
Draw. Import the photo. Activate the Interactive Dropshadow tool, and select an halo preset.
PhotoPaint. Open the image. Activate object in Object Docker. Right Click object name and select "Create Mask from Object". Mask menu Mask Outline/Expand. Select as many pixels as you like your halo width. Create a new object/layer. Fill it with the color you please for your halo. Delete the mask and apply Gaussian Blur to taste.
You could use the Interactive Dropshadow tool in PhotoPaint.