Yup - it does seem to be a stock photo.
However, I believe she is a bit like the alternate haired Cupcake and at least one of them must exist - 1) for the promo shot and 2) because the green dress version does have "real life" images from one Taobao seller. But this could really be all the same pony who went from promo shot pics to a seller or perhaps a small run of her was done but in incredibly small numbers. I know one person who ordered this "green dress" FS from that seller stressing the importance of that version but the seller could only supply the pink dress versions. So he probably had one and as that was the first one he got, he just keeps reusing the same picture.