This seems to have been girls' night in the Arrowverse. Both tonight's Legends and this one focused on the female cast members teaming up and bonding. And Sara Lance was on both teams. It might've been nice if the LoT episode had had some brief nod to Sara getting a call from Star City at the end. But hey, she has a timeship, so theoretically this could be the Sara from weeks in the past or future. And of course there's no requirement that two episodes shown on the same day had to take place on the same day.
Anyway, Sara's inclusion was valuable to the story, engaging with parts of her Arrow backstory that rarely come up on LoT anymore, and paralleling her experiences with Laurel-2's. And we got that great scene of her in a tank top using Oliver's salmon ladder and looking amazing. Wow, those biceps.
Apparently this new female version of Shadow Thief, Aviva Metula, was introduced in the comics in 2013, although the comics character has an alien suit that gives her shadowy superpowers like her classic namesake, while this one's just a, err, shadowy thief and mercenary.