Thank you for your advice however I'm afraid all of you suggestion would not work on her since we have tried. But thank you so much to take the time to try and help I really am thankful.
I will try to answer some of your questions, understand though, I am a mother of a DS son . he is 38 now, plus I worked in the field of adults with disabilities for 20 years and am a RN. As far as the toothbrush thing, that is showing independance. Give her the toothbrush and let her place it down. As for the sitting down, try reverse physchology, tell her, don't sit down, just once and then leave. Never have a 2 hour battle with her, that is for attention. Talking to herself, tell her you will let her alone so that she can talk and if she wants to talk to you, you will listen. A DS child has a remarkable memory usually, use it in the training, when she is learning something, ask her to tell/show you back. Is she around other autistic children at school, they are great copy cats, my son did this, we just didn't call attention to it and the practice faded away. A DS child is smarter then most people give them credit for, sounds to me like she might be testing you. Ignore what you can and give positive reinforcemnet for a good job. A trip to a child physcologist might be a good idea, but make sure they know who and what they are dealing with. If she is in school, make sure the special ed teachers know how to deal with her just the way you do at home, that will create less confusion for her. Good Luck I do not know of any DS that has ever had a multiple personality disorder.