She is people, a woman.

Dollhouse S01E03 releases an episode where Echo is not a doll,she becomes a real people.She is out of others' control,she thinks and does something not imprinted.
She is evolving,in my guess, and she may be remembering every imprint and her momery may not be cleared away. She is a miracle which gives her handler Boyd and their doctor and ever her boss Dewitt hope, hope to fight against Alpha, a big threat once running away from Dollhouse,and something else. After all, the boss is excited to find Echo's such ability.
In th final, Echo and Sierra are looking at each other knowingly while walking across.Echo winks at Serra not to approach her as a friend but just to walk on as a stranger.
The story of Echo with Jayna itself is good,but what most impresses me is that Echo is not a doll that can be completely controlled. That makes this article.