She's just able to pull it off coz she's gorgeous, so she does it lol, I have a mental image whenever I think of Trampus my Deerhound of him standing on a hill looking around at the rabbits (yes just at them, no chasing), when he got called, he just put one ear up as if to say yes I'm listening but stayed where he was watching the rabbits lol.
Yes I think she only puts one ear up when she is doing the woman thing and listening to 2 things at once , you get both ears when she is really focussing on something !