Arya Will Wear Littlefinger's Face

HBO

As we saw with the demise of Walder Frey, Arya Stark now has the ability to wear people's faces which she learned from the Faceless Men assassins. After executing Littlefinger in the season seven finale, it doesn't seem unreasonable that Arya would wear Littlefinger's face to gain access to King's Landing.

Even if Littlefinger isn't welcome at King's Landing, it would still get Arya much closer to the people she wants dead down south rather than if she appeared as Arya Stark.