So Emma is a Dark One, but she went into it already strong with light magic, so that gives her an advantage, does it not? Helps her with control? Dark Hook, on the other hand, is like most other Dark Ones — no previous magic, totally embracing of the shadows, except for wanting to kill Emma. He’s shying away from that still, so even though he’s furious with her, there must still be love . . .
What if Emma pulled out her heart and separated the light from the dark? Split her heart in two, the same way Regina split Snow’s heart to save Charming, and gave the good half to Hook? Would that help him to fight his Darkness?
Or, what if she froze him with squid ink and pulled his heart first, then her own, and switched them? If she put her Light in him, would that save him? And enable him to save her?
If the best thing is to get back to having only one Dark One, Emma giving her Light to Hook after pulling out his Dark heart might be the best solution. Except for it destroying her . . .