About that smirk...(spoilers)

[Cilia]

So, tell me, when Tataru twists that dagger in your back, how back is it going to hurt you?

I'm a dark knight.

I've accepted that today's allies may be tomorrow's enemies; this actually happens with the Church in 3.0 (though how much the Church could be considered an ally is tenuous at best).

If it comes to that, I will do what I must.

Until then, there's no reason to suspect Tataru of wrongdoing. The only thing supporting that argument is an interpretation of her words and a smile, neither of which are concrete evidence and that viewpoint does not match up with her characterization.