I hope the writers approach it differently than they did with Lance. He used Earth-2 Laurel as a do-over, seeing her as his actual daughter instead of a mass-murdering transplant from a parallel world. Obviously he was understandably very emotional and irrational, but, I would prefer Sara seeing her just as someone who looks like her sister. She can absolutely get to know her, and even relate with her on all the killing stuff**, but she should never, ever call Siren "sis" or "sister".
And if Earth-2 Laurel dies and Sara is upset, she can always pull a Lance and substitute her with Earth-X Laurel
** On that note, I see some chatter online about how because Sara has also killed people, that Siren is no less deserving of redemption than she is. Now it's true that she has, but, as far as we know, Sara never enjoyed killing people during her time in the League. And she's actively worked towards being a better person, wrestling her demons every step of the way. There's an effort there that just isn't present with Siren, but that could be on the books for next season. Still, we've seen Siren smile in a woman's face, kill her, steal her shoes then gloat about how she killed her to another woman she's tried to kill repeatedly. This is of course before the writer's dropped her sadistic personality in favor of Diaz's lack of volume control.