Arrow - Spoilers galore

Soundwave said

I'm thinking it's Earth 2 Laurel. She was left behind after they defeated Zoom IIRC.

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I believe she was last seen imprisoned at STAR Labs.

Earth 2 Ollie died on the Queen's Gambit. If they had the same relationship, it would explain E2 Laurel going evil, and then seeking out Ollie on Earth 1.

I actually think I really like this scenario.