Looks very realistic! Though I think the belly button should be a little lower (and the curve itself too). Also, the shading "down there" is somewhat off, looks almost like a penis coming from her tummy. Basically the color/shadow transitions at both sides should be a little less sharper than they are now. And the buttcheek is too far out, it doesn't look like she has that bone structure.
hmm, I disagree somewhat. regarding shadow, I actually think it looks realistic since this is both away from the most lit spot in the image and also the skin is thinner with blood concentration ergo, appearing darker in this region. For the buttcheek, unlike the male pelvis, the female one is usually slanted at about 60˚, which takes the bone and respective muscle/fat tissue also stick further out in relation to the rest of the body, which is why to me it looks like she has that bone structure. Of course, it is more pronounced in some individuals than in others. I don't think your points are not valid but I think it's more of a personal approach than anything. Hopefully, I am not wrong