I enjoy that about the Flash too, but it sure would be boring for me if Harrison Wells wasn't the bad guy. But I do agree Arrow could use a few episodes of that too, to make the conflicts matter more. That's still different. You have the advantage of not having a story she is supposed to fit into, so you can craft a story that "just so happens" to require her. However having a need for a bat-character doesn't make her the best candidate. It still makes more sense logistically to bring over someone from the packed Arrow squad or a reformed Assassin, they'd still have the requisite baggage, but not the baggage of a resurrection storyline which doesn't help the story you're pitching. The best choice in that scenario, honestly, would be Deathstroke. If I were doing it, and again, this is creating a story from the ground up that requires her, I would focus on Rip Hunter's mission, one that involves multiple/alternate realities, and pull a Sara who never died from such an alternate reality, a reality that plays a role in the upcoming events. I think that's the Sara fans want anyway, not some hackneyed retcon. They want Sara to never have died, so... give them a Sara who didn't. Go one better: in her reality, Laurel died! Instant faves. That fact can be a large or small piece in the story later, where Rip Hunter's plan revolves around her being from an alternate reality so she's not affected by MacGuffin X, that she's 'the chosen one' in that sense. In that way, she is the best possible character for the story. There are other stories you can create to do the same of course.