Anyways, the first thing she says is "You're alive." This implies that she thought the Inquisitor was dead. Before you open the door, the torturer tells her, "There's no one left."
If this was simply a mission where Leliana was sent to assassinate someone, she failed, and was captured, why would she believe the Inquisitor had perished?
Dorian says, "You aren't curious how we got here?" If it were simply a matter of them riding to the town and killing people as they made their way to the castle, I don't think he'd say that.
On another note: the female qunari is so tall. Look how she just towers over Leliana!
You know, the more I rewatch that video, the more I'm starting to believe that is where you officially recruit Leliana.
My theory is that Cassandra and Leliana take the Inquisitor captive after the explosion at the Temple of Sacred Ashes and try to get answers about what happened. Soon after they get attacked by Alexius' men. Cass and Inquisitor manage to get away, while Leliana and the others try to hold off the attackers and fail. The Tevinters kill everyone, subdue Leli and bring her to Redcliffe.