Why do some people look fantastic at a particular weight and not at other weights?

For example: I am very proud of my friend for her weight loss. Everyone said she looked fantastic at 150 pounds.(She was 200 before). Now she's 120 pounds and even her family thinks she looks kind of...sickly? Why is that? Even her husband was concerned and asked of everything was okay.

I've seen this happen a lot and I'd just like to know why this happens.