Dragon Plays with Fire - S1-E13
Continuity mistake: Danny grabs the keycard off the guard with his left hand. He still has it in his left hand outside the elevator door and when going inside. But it's in his right hand when he puts his hands on the back elevator wall.
Answer: Sokovia is a nation in the Iron Curtain. It is just as likely for a US operative to end up there as any of the other former Soviet nations. There is no reason to believe she was there at the same time as the Avengers. It was likely some form of covert mission there years beforehand.