She looks like a bodybuilder to me. dh used to be seriously into bodybuilding, and anyone who thinks it is a healthy lifestyle or does not involve yoyo dieting is really very naive. Not only do you have to have high levels of targeted exercise, weights etc but in order to get that shredded look you have to both starve yourself and be very dehydrated, and it's generally only possible for a few hours. Which is quite dangerous (including documented deaths). There are also tricks with make up etc to get the appearance of more definition.
Of course you can naturally have very low bodyfat. My ds is very very thin (off the scale on BMI) but there are drawbacks - ds gets cold very quickly for example, we hope as he goes throguh is teens he will start to fill out a bit. It's also not something that you can just naturally become, being very thin is either genetic (like ds), caused by illness or stress or the result of concentrated effort and control (including chemical control).
So yes an eating disorder could be involved (many body builders have some degree of body dysmorphia) or pressures of the industry you are in.
Either way it's sad because she looked really very beautiful and much more healthy not very long ago, so you wonder what drove her to her current look.