Well come to HCM Thank for asking Appreciate your concern, what the degenerative disease your sister has it is just nothing to take anything with the condition of constipation, with the history of constipation blood stain stool is very common or bleeding per rectum also common, (It is not being stated here that it was the blood from the rectum or it is the menstruation) in either of this case it is nothing to worry, but try to encourage her for drinking water, leafy vegetable diet, once the person eat something or having food by mouth then it going to form the stool, so it is not the case as you are thinking, hope this information helps.