I think the issue for me is the placement of her hands. Marilyn was pushing down on her dress, which is coquettish and cute. Your model is holding up her dress (probably from flicking it up) and almost looks like she's reaching for her crotch. Combined with the turned in knee, she kind of looks like she's imitating a toddler that needs to pee. It's a tiny thing, but for me the whole photo depends on getting the posing just right. The legs and positioning of the dress would all work if only she was pushing down instead of holding up her dress.