Download the PSD file
Basically, I first added the gradient layer and made it the colours you'd shown me, and masked it but only very roughly, and not too close to the subject.
I duplicated that layer, and changed the bottom one to Overlay mode, then made its mask completely white, then modified the gradient colours to make it match the top layer as closely as possible. This part was hard, I went back and forth quite a lot.
Then I more carefully masked both layers.
After this, it's up to you. On the top layer, you zoom way in and use a tiny brush, to mask out the hairs you don't want.
I did a small section to show you: