Now that the junk food is out of the way (absolutely no soda pop, no sugar, no white flour; that sends her crazy bio-chemically inside) and your daughter can better track with you, let's address the attitude problem of your daughter.
If the aim of adulthood maturity is self-denial (which it is spiritually for all of us) then you must train the will of a child to be able to put itself under for the good of others, and to be crossed and denied and to respond with a magnanimous spirit.
To begin with, she has to want to live. Therefore, her spiritual life must be strengthened. She must feel that she has value before God or she will give up and act out. Start with helping her cultivate a strong devotional life. Help her underline in her Bible daily, making it her own workbook, writing down just one thing out of ten minutes of Bible reading. In addition, she must have something that she does well; to give her self-worth, that helps define her. Find out what that is and plus it and develop it. (It may not be academics; it may be a skill or a talent or a unique social contribution or speech making or....) If a person feels like a zero, he/she will act out. A person must feel validated in his/her existence, to want to work on his/her behavior.
Secondly, a person must see his or her current behaviors in others, in contrast to regarding more noble behaviors in others. Ask her what draws her to other adults; who does she like among adults? Why? Show it to her outside of herself--both in real life and through biographies. Biographies are seldom written about self-absorbed or selfish people. Teach her that to be loved one must strive to be loveable. An adult doesn't just wake up a good listener or kind or....; they started working on that attribute as a child. What you are now is what you will be as an adult, unless you put into yourself different behaviors. Habits of behavior are almost unbreakable for us as adults; it is important that she get serious about the type of person she is becoming now. Each day she is creating attitude habits in one direction or another.