As referenced in this episode, Sara Lance is running around pretty much fine after her dip in the Lazarus Pit, while Thea's bloodlust is curing itself by killing the host, leaving her in a coma by the end of the episode. The difference? Constantine brought Sara's soul back, and didn't do the same for Thea. The question that just seems to be hanging in the air now, then, is why not? Why, when he's doing all of his magic, couldn't he just happen to cure Thea as well? There's probably an obvious answer in there somewhere, to do with Sara being properly dead, but it just seems like a complete oversight that the writers haven't at least acknowledged that fact.