This may sound like it's coming out of left field, but has anyone considered that your sister may be having a psychotic break? Please don't freak out here, but the signs point to the possibility of a schizophrenic episode. Schizophrenia is a disease of the brain -- it is not a personality disorder or a character flaw or the result of bad parenting. It is simply a biochemical disorder of the brain that has an onset in women during their early twenties. Prior to the onset, there is a "prodrome" stage of strange behavior, reclusion, introspection. The Natioanl Alliance for the Mentally Ill has lots of information on schizophrenia. So does the Schizophrenia Society of Canada.
I'm not saying this to alarm, but it does strike about one in one hundred people (for men it's usually in their teens, and for women early twenties).
Strangely enough, taking up smoking is very common during the first psychotic break. So is lack of personal hygiene, putting on weight, and a slouching posture. Bizarre thinking is also common, as well as an emphasis on how others are out to get them. sometimes they hear voices telling them bizarre things. The most telling symptom is a bizarre and rapid change in personality -- particulalry not caring anymore about things (and people) that used to be so important to them.
The good news is that there have been great advances in medication, and the sooner it is started the better the outcome.
I recommend that you follow all the other advice posted here and try to get your sister checked out by a competent doctor.
Good luck.
