The actress is slated to appear in at least one episode this November, although the character's name is being kept under wraps for now. It hasn't been confirmed whether Felicity's mother will appear in present day Starling City or in flashbacks, although Arrow executive producer Marc Guggenheim revealed to TV Guide that they are telling "the secret origin of Felicity Smoak" in Season 3.
"We are absolutely going to get to know her. We know that she went to MIT, we know that her mom was a cocktail waitress in Vegas and we're going to meet that mom. And we also know that her dad is not in the picture."
Charlotte Ross joins a growing group of new cast members this season, including Brandon Routh as Atom and Karl Yune as Maseo and Devon Aoki as Katana and J.R. Ramirez as Wildcat. It was revealed during Comic-Con that the Felicity-centric episode will be dubbed "Oracle," although it isn't clear when it may debut during Season 3. Ra's al Ghul was also revealed as the main Season 3 villain, but he hasn't been cast at this time.