Has anyone sought to speak to a doc about her? It is all well and good looking up symptoms on the net , but it is not going to help you to be able to understand/cope , and it will not get her any help either. Please , even if your sister does not want help , go and get help for yourself. I would encorage her husband to go along aswell , it must be really hard for him to see her this way. They will also be able to suggest what steps you can take next.
BP? I couldn't say - even the professionals have trouble diagnosing this one.
Take care hun ,