I have a friend who was a runway model in the early 1990's in Europe. She did a lot of print modeling for designers here in the US as well. She is naturally very thin and tall with a crazy fast metabolism so she could still eat. The other women hated her. Lots of people living on coffee, cigarettes, diet coke, stimulants, sleeping as much as possible because they weren't eating, chewing on a piece of meat forever and then spitting it out. You get the idea. To be that lean, she said most of them didn't exercise. They did the eat less/ move less method. When she moved from runway (clothes hanger thin) to more print work, she had to get breast implants so she'd be more curvy.
Re: unhealthy eating habits. You see this kind of thing a lot in the dance world. Women dancing long hours and living on sub 1000 calories per day. Stress fractures and loss of normal hormonal function are common.
Re measurements: You said 25-27 waist/ hip? If that's a waist, it's not at all unusual. I'm a munchkin, and have a 23-24 inch waist when I'm leaned out. It would be nearly impossible/ very rare for a mature women to have hips smaller than about 32 inches just allowing for normal hip bones bones post puberty. 33-35 inch hips will still put you in the smallest clothing sizes.
I'd tell your friend not to get involved in this.