Mia said that she recognized this new Canary from the documentary filmed back in the 150th episode, so it’s pretty likely that this is the reformed Earth-2 Laurel Lance, returned to Earth-1 to help Felicity’s daughter.
Fortunately, a save came in the form of a Katie Cassidy Canary blasting the baddie away with her cry.
The final flash-forward of “Lost Canary” saw Mia facing off against a very dangerous enemy who caught her by surprise before she even got to try a sneak attack.