^^ It's worth noting that Amy was also a 'Ganger' at the time...
I don't think she was. I was always under the impression that she was captured & replaced by the Silence sometime during the long gap between "The Impossible Astronaut" & "Day of the Moon." That's why she thought she was pregnant in "The Impossible Astronaut" but thought she wasn't in "Day of the Moon."
EDIT: And wamdue
beat me to it.