I was re-reading the thread and I see that you analyzed the quote to be about Arya, but it's about Sansa. Sansa is the one who recently disappeared and the daughter who Brienne is looking for. Jeyne Poole had been sent North as Arya Stark and wed to Ramsay Bolton. Brienne has been wandering near the border of the Vale and the Riverlands for some time, trying to find Sansa, as Jaime and Brienne are under the impression that Jeyne is the real Arya. The only people that do/did know about fake Arya are Roose Bolton, Cersei Lannister, Tywin Lannister, Littlefinger, Varys, and most Northern nobility.
Also, the Greatjon has to break out of the Twins to go do a Queen in the North speech for Sansa. And then she has to bite off his other fingers.