Right so as I said as soon as I managd to find the Flash episode in hd somewhere I'd share my newest catch. Here we are.
I was worried about body doubles but I don't really see too much of a difference in the feet between the pictures in where you clearly see Melissa's face attached to the feet and in those where you only see her evil twin version. So I guess they played around a bit and managed to get both versions of Melissa in this shot without body doubling.