what could cause my 10 year old daughter to hoard food and bite herself when she!

I was told she may have bipolar disorder but I have it as well as my mom,brother and nanny. None of us hoarded food. I have another child with a mild form of Autism and Schizophrenia. Is it possible she may have Autism. She did not start talking till after three. We had to get her to a therapist for that when she did start talking she had a british accent. She has a very hard time with changes, but I thought at first it was do to some issues with me going to work and her dad getting ill. We are seeing a therapist but she does not talk about any problems, she just says what she thinks everyone wants to hear. She aims to please everyone else, but we have to deal with the bad mood swings, persistent lying and constant clearing her hiding places of food and junk. She is not denied any food and I try to make a point of doing a Special day for just her at least once a week or two. taking things away, time out, extra chores, and even every type positive reinforcement has been tried but nothing seems to phase her. She even adopts the attitude that what ever she was restricted from, she didn't want or need anymore so it does not matter to her. She gets upset at any type of criticism good or bad. She says everything is her fault and she is not good at anything. we are always praising her and telling her how we love her but she does not believe it. I need some help on this. She has even started to fall behind in school, because of all the things she complains about hurting her and being sick to avoid school. i even tried to home school her for a year to see if that is what she needed. She only lasted at that for 2 months and wanted to go back to school.