Not to get into my thrilling life-story-thus-far, but I was pretty messed up with anorexia, then bulimia, THEN the combo of bulmarexia in my late teens/20’s…and a bit '30’s, although I’ve been ‘retired’ for over a decade now.
I wouldn’t presume to diagnose your sister (I’m not a professional, and even a doc or whatever would have to see her in person).
But, it sure does sound like she is somewhere on the eating disorders spectrum; I feel that many, many women are somewhere on that spectrum…anywhere from just thinking they are a bit fat, to full-blown anorexia/bulimia.
Your description of your sis indicates that she is at least leaning towards anorexia, with the good/bad food and restricting food, along with the rigorous excercise.
At 17, I was a lot like your sister. The earlier some kind of help is sought, the better-although eating disorders have a reputation of being challenging to treat, like most ‘addictions’.
When you’re anorexic, you feel you are controlling at least one big part of your life; often the person is basically trying to suppress stress/anxiety with the food ‘rituals’, and often accompanying exercise.
The sad irony is that the anorexic/bulimic may feel triumphantly thinner, while in fact their health is at risk, and they are actually a slave to the disorder rather than being in control. So, I’d say some action from your family is definitely in order, while cautioning you to tread carefully.
I clearly recall how it feels to be that confused person…and someone on this path most often resents any interference, and in fact will go to great lengths to deny any problems, or hide them. Although deep down, the person with an eating disorder may be aware of the illness, most of us are not keen to admit that anything is wrong.
Every individual has a unique ‘pathology’ of their illness/addiction; each person is different, has different aspects to their disorder, and will [eventually, in most cases, with any luck…and professional help] improve in their own way.
When I was in ‘e. disorderland’, there was not that much help, especially in rural areas. In my opinion, it’s still much easier to obtain treatment for alcohol/drug addiction (I remember actually wishing I was an alcoholic instead), but there IS help out there.
Before any family member approaches your sister re: her eating etc., I would STRONGLY encourage you to do some research i.e. google ‘eating disorders’ on the 'net, consult healthcare professionals if possible. Throughout my experience, I saw MD’s/psychiatrists/nurse practioners/psychologists etc.
Some people were very helpful, some were frankly pretty awful; it depends a lot on trust and personality, and everyone is unique, of course. Your sister may have a more easily treatable ‘pathology’, or she may be more of a hard case. To get started, I’d run-not walk-to research things.
Get an idea of what ‘treatment’ may be available in her area, and have a family member meet with or at least talk to a professional to figure out how to best approach your sister. As with many illness/addictions, e. disorders are really a FAMILY problem, especially if the affected person is still living at home.
This is NOT to say it’s anyone’s fault in particular…simply that family dynamics play a part, and must be addressed if treatment is to be effective. Eating disorders really screwed up my life in many ways for quite a long time, but most people recover to a large degree. I paid a price, but am sooooo glad to have found a more normal life again.
I wish you and your sister and family all the best, I truly do.