Remember how Cersei said her fate was to be decided by a
Trial By Combat ? Now remember, Arya being specifically questioned about the Hound's death and his character been given more importance than Cersei, Walder Frey ? Piece those two together. Could we see a Mountain vs Hound combat ?
Dead vs Dead ??
Just thought of another way this could be dealt with. That constant questioning by that unlikeable lady about the Hound might also indicate how Arya feels about him and whether she is ready to assume his identity. If she is and once her training is complete, she might assume the identity of the Hound (I don't know if this face swapping thing only works with Alive people or not tbh) and go after Frey, Cersei, The Mountain.