This is a story related achievement and can't be missed.
When you're done climbing the Origin Tree in Kashyyyk, you're gonna ran into the Ninth Sister. She is actually easy to fight, you just have to use one sided lightsaber to deal the most damage. She has some pull and push force abilities and switches to dual bladed lightsaber after a while. Just be careful of her unblockable stomp attack that makes the ground comes like a wave to you. You can jump to dodge it. You'll unlock the achievement once the fight is over.