I think the peace sign was pretty much invented in the US during the 1960s hippie movement. It's never completely gone away and I still see it used by people. I notice young American actresses flash the two fingers in photo-ops from time to time. Just something cute and harmless to do to spice up a picture instead of standing there smiling with your hands at your sides.
I guess it's a phase Maria's going through, like with her pajama pants.