This is definitely my pet crack theory, but is it possible that Ashara’s child is still alive, and is being kept hidden to help give out the suggestion that Jon might be Ashara’s son? Barriston Selmy specifically believes that the stillborn child was a girl. For this to be true the child would have to have been introduced already, and the only character I can think of who might fit in this picture is Mya Stone, since Jon Arryn would likely be willing to keep an eye out for Ned Stark’s bastard.