In the first one, there's apparent flattening caused by the light from nearly overhead (which would place shadows below) and the drape of the dress, which eliminates said shadows. She looks rather more flat chested than she is. Also, she has extremely narrow shoulders, which increases the appearance of skinniness. Possibly she has them rotated a little to make them appear narrower, as well. I'm not really seeing it, but it's hard to be sure.
The proportions are just fine, her navel's just much lower than you think it is: nipples one head-height below the chin, navel one head-height below that (almost at the bottom of the frame). This is how people are made.
I actually have no idea from the first photograph how skinny she is. There's basically no information there, other than "not portly". The photograph certainly uses styling tricks to suggest a cadaverous appearance, which is a reasonable point to make. No point in slamming the girl for a couple of optical illusions, though.
![[No title]](/data/xfmg/thumbnail/35/35967-ee5e7220e6f5cbd7d70fb99fe8ce5038.jpg?1734167844)
