It sounds like jealousy and competitiveness, and that she is toxic for you. I think you should distance yourself away from her as much you can, and not tell her anything as much as you want to. It's better to tell a counselor. It would be better if you weren't in the same room as she is in. It sounds like she is trying to help you have your own life without her, and she doesn't seem to want you as a sister all that much except when she can order you around because she thinks you're mentally handicapped and not capable of handling yourself. She's probably trying to change you as a person too. I'd go to a counselor or a social worker asap. It seems like maybe your mother paid more attention to you than she did her because of the extra help you needed. I wouldn't go to your sister for help again, and I'd tell your parents if you can. I'm sorry you have a sister like this. A person who nitpicks you all the time and with whom you can't be yourself around isn't the type of person you would want to spend time with anyway. I think you need to join a volunteer group or anything to get you out of the house so you can have a better chance of friendships and social life apart from her. You can join forums that specialize in any interest you have too.