Its disturbing at how many are actually being conned by Arya [Warning Spoiler]

• When she came back home she was happy to see Sansa and they had a moment. - This was before Arya knew that Little Finger was there.
• Arya isn't a naive girl anymore and after her near death she clearly has improved. Such as her using her skills to fool the Freys.
• Arya can change faces, yet she isn't using that ability currently.
• Why? Because Little Finger doesn't know she can do that and she WANTS him to see her, Arya Stark, snooping around.
• Arya has enhanced senses from when she lost her sight, she knows that Little Finger has been following her. Its also been mentioned that Little Finger has a certain scent, most likely the only one there who has that type due to his wealth and connections, thus easy for Arya to track with her enhanced sense of smell.
• Little Finger doesn't know that Arya was trained by the faceless men. Based on what he knows he can only assume that she has no real training hence why he doesn't question why she's acting so sloopy and obvious.
• Arya is pushing Sansa for two reasons which are to confirm that she isn't completely manipulated by Little Finger and to trick Little Finger into thinking that his plot is working.

Arya is playing the long con.

Don't be surprised if Little Finger ends up executed by Sansa in the next few episodes due to Little Finger, vastly underestimating Arya due to his lack of information on her, falling for Arya's plot.

This also will push the Vale to choose as they openly told Sansa that they're here for her, not Little Finger.