Got this in my “All Heart decisions” playthrough. So just pick the heart options whenever you play as Taylor. It popped for me when I got to the tire swing and after Daniel says he believes you about the tire swing being yours, pick the heart option on the right rather than the left.
If it doesn’t pop here for you, another major boost to the Headstrong trait is after you run out of the church and Taylor is by herself on the road. It will give you an option to either go left or right. Go left and survive the encounter with your demon for an increase in the Headstrong trait. Going right will make you find Andrew and doesn’t add anything to Headstrong.