Arya's eyes are sharp, and she is able to get a good look around the room. However she can't discern much more than what Taruviel and Nyssa have already uncovered as far as the footsteps go. She also doesn't notice any kind of tripe wires or pressure plates that would suggest traps. Perhaps the Dollmaker had not seen fit to boobytrap the very front of the house, as it would no doubt give off a paranoid impression to guests.