Meh... I Disagree. Arya is not gonna kill her own family.

Not when there's so few of the Starks left nowadays. That's not her style.
Arya RIDES for House Stark.

Please Believe.
Any chic who (singlehandedly) executes a
WHOLE BLOODLINE of family enemies, in the name of justice... is not someone who is going to kill her own sister.

Not at all.
She would never kill Sansa... but she would definitely
EXPOSE the shit outta Sansa... to the fullest.

And let the chips fall where they may.
My theory....
In the lastest episode 6... I noticed that Sansa has really started to revert back to her super-spoiled, bratty, selfish &
eager-to-be-royalty old self, from season 1... So Arya will expose that is her
'true nature'... and what she has
always wanted all along.
Sansa was literally BRAGGING to Arya that Jon lost the Battle of the Bastards & the Knights of the Vale only helped out... BECAUSE OF HER.
That was FOUL.
Because Sansa could have gotten the Vale 'to help out' right from jump.
But she LIED to Jon about them.
And LIED about the Blackfish.
For no damn good reason. At all.
Why the fuck was Sansa making shit harder... especially when Jon is trying to kill the fucking guy who made her life miserable? 
And when there was no more allies left to gain in the North... she had to BEG Littlefinger... at the very last minute, to come back & help.
That's NOTHING to Brag about.
Stay in your lane. 
Without saying the exact words, Sansa pretty much told Arya: "That was MY Victory. Not Jon's.
Bet I could rule this town much better than Jon ever can."
And Arya read her response correctly.

She can see right through all of Sansa's bullshit ambitions to be a Ruler. (Like Cersei.. who she 'respects'.

)
Meanwhile, Sansa is playing right into Littlefinger's trap. Like a dumbass.
Letting her EGO get in the way of 'thinking smart'.
Right now Sansa's
1st biggest mistake is thinking she controls the Knights of the Vale... because she thinks she can control Littlefinger... just because he wants to smash.

But Littlefinger is a brothel-keeping MASTERMIND.
HE BEEN RUNNING GAME ON BROADS & PUTTING THEM ON THE STROLL... FOR YEARS... FOR A LIVING.
Sansa is not on his 'deception level'. At all.

He been 'taking it easy' on her all this time.
Filling her head with notions of Ruling Shit Together... when all Littlefinger really wants to do is get some
'revenge-booty' from any female Stark family member (because they have always rejected him

).... and keep it moving towards the Iron Throne.
If Baelish really 'laid his game down flat'... Sansa would probably be out HOE-ING around Westeros. And bringing all them gold coins... back to Daddy.
And her 2nd biggest mistake... was sending Lady Brienne to Kings Landing... and demanding that she take Podrick along.

Leaving herself completely VULNERABLE to a rebellion... with ZERO backup if Littlefinger convinces the rest of the Bannermen to rise up against Jon.
Arya knows that Littlefinger can take control of Winterfell... in a heartbeat.

And Sansa would be completely helpless to stop him. (Especially after Brienne rides past those gates.

)
So Arya is using.... Jaquen H'ghar tactics on Sansa.
The same way Jaquen gave Arya
'murder assignments' in Braavos, to prove her
'true loyalty' to the Many Faced God... Arya 'laid all her cards on the table'.... then gave Sansa the Valyrian Dagger... so Sansa could atone for her past selfishness.

And prove herself 'loyal'. Once and forever.
Basically, Arya acted like Jaquen H'ghar... and gave Sansa a
'murder assignment' to kill Littlefinger, to prove her
'true loyalty' to House Stark... which should be VERY EASY for Sansa to accomplish (but Sansa will obviously fail to do it.

Because deep down inside she truly wants to be a Ruler of.... 'something'... like Winterfell, or the North... or Never-Never-land.

and she will always keep the people 'close by'... who she thinks might help her accomplish her dream.)
If Cersei were in Sansa's position... she would've killed Littlefinger herself a loooong time ago.
But Sansa keeps him close by (like a dumbass)... in case he can help her out... when its convenient for her.
A man like Littlefinger won't wait forever on a leash.

But Sansa thinks he WILL.
Soon enough he will just TAKE what he wants.

By any means he has at his disposal.
So once Sansa FAILS to kill Littlefinger... (which she will)... Arya will just do it herself.... Plus
'air Sansa out' (once & forever), at the same time.
Arya will probably kill someone who can easily get Littlefinger alone in a room somewhere in Winterfell, or deep in the Tombs.
Someone like...
This would also 'clear the path' for Sam Tarly to become the new Maester at Winterfell, in the future.
Then Arya will expose all of Sansa's fuckery to Jon... and suggest he give Sansa what she's always wanted....
To be Royalty... Married to a Prince.
Wait for it.
