Nope! In fact, she's not Christian at all — she's Jewish!
According to IMDB, as a child Ginnifer attended a Jewish summer camp, and apparently during a recent Marie Claire interview (via San Diego Jewish Journal), she and the interview writer got to talking about their heritage, and discovered there may be a connection between Ginnifer's grandfather and the writer's local synagogue. Talk about a small world!
Once Upon a Time airs Sundays at 8 p.m. ET/PT onABC.