Help with Uncontrollable Teenager

My girlfriend and I are at our wits end and don't know what to do. A little backstory, my girlfriend and I met about a year ago, fell in love and decided to have a baby together. When I met my girlfriend she currently had an 8 year old son and a 12 year old daughter that I consider my step-children. The point of concern is the 12 year old girl.From what I've been told she has a condition called Intermittant explosive disorder, a psychology disorder she recieved from her biological father. This causes her to have a short fuse and explode through violence and aggression over even the most mudane things. The only medication that is suggested for her is "intuitive" I think thats how its spelt. Which we tried and did nothing for her. But what I want to focus on is two particular incidences that I was actually present for. These were the biggest incidences among multiple minor explosions.First one happened about a month ago, it started after she asked to have a sleepover. Her mother said no and this all escalated rather quickly to her saying some of the most disgusting things I ever heard a 12 year old say. (Go burn in hell, I hope you die, I'm going to kill you in your sleep, not to mention a vast collection of curse words) This resulted into a confrontation in which her mother told her to exit to room, she refused to, I stepped in by lifting her up and carrying her to her room. She claimed I abused her and called the police with the new iphone I got her. (Im such a horrible step dad right).The second incident happened yesterday, we both saw it coming. You can see the build up of a explosion like smoke from a volcano before it erupts. She craves the conflict and its only a matter of time before she explodes. Well after recently moving into a beautiful new home my girlfriend and I established one simple rule: No eating in the living room or bedrooms. One rule the 8 year old has no problems following, however, the 12 year old has been trying very hard to break this rule. She was caught 3 times already and was warned, she tried bending the rule by moving the rolling chair to the edge of the dinning room and living room and eating there until I moved that chair into the attic.Well yesterday was my last straw, after spending the entire day treating her and her brother she decided to eat her treat in the living room in front of the TV. I approached her and asked her 3 times to eat at the dinning room table, she ignored me. I snatched the food up and said it again. She rolled her eyes at me and looked away. So I turned the tv off. She then said "Don't you dare turn off the tv on me or you'll be sorry" this immediately boiled my blood. Nobody disrespects me like that especially a 12 year old. I ripped the xbox from its cord and tossed it onto the couch. Well this escalated into her explosion where she said some of the most disgusting things I've ever heard ANYONE say. Saying im a horrible father, her biological father is better (which let me just saying Im holding my tongue from discussing him in this post I'll tell you that) I shouldn't be with her mother, and even said that she deserves everything in the world (a statement she seems to live by) and then spitting out a collection of lies. She is a pathalogical liar, a habit we are trying to correct. These lies can vary between well thought out the completely rediculous. This particular incident her lies were just beyond rediculous. Ranging from "She was going to eat at the table but I was in her way" to "She was confused and didn't understand what I was asking her". When I wouldn't tolerate or give into her she turned her attention on her brother, on her mother, and even on the dog. When the front door opened she said she hopes he gets hit by a car. When she saw that my girlfriend wasn't taking her side she exploded even more, her words worsen and worsen. She threatened to run away which we told her if she did she isn't welcome back, so she resorted to hiding in her room. Now there is a 6 phase formula with her that I've come to recognize:The explosion phase: Initial explosion involving physical violence and vulgar languageThe storm away phase : She storms off, either runs away or into her room. This is where she plans for the next stepMalice phase : She intends to emotionally hurt as many individuals as possible, even with passive aggression.The Victim phase: She returns claiming she is being victimized, stating she is the black sheep, she is being abused, that there is something wrong with her and its out of her control.The Nothing Happened Phase: She returns happy, playful, and upbeat claiming nothing of importance just happened. It was "no big deal". This phase is replaced with a worried weeping if there is a chance that she may have actually hurt someone.The remorseful phase: This phase is where she resorts to almost a child-like demeanor and is remorseful and apologetic. Wanting to hug and cuddle. Now her mother and I both know she isn't actually remorseful, she just hates the silent treatment we give her. It's one of the most affective weapons . We call her out on it which results in her storming away a few more times in anger before we just let it go and "believe her".Anyways Im here to see what advice I can get, also what I personally should do from here. Im not ready to forgive her and with the way she treated me and the things she said I don't even know when I'll be able to. It has become a known fact it will happen again within a month or so, I don't know how to react because today is my birthday and I know she will want to be involved in the celebration but I personally am not ready to forgive her, and I cant forsee when I will be. Her behavior makes you see her in an entirely new light. The sweet, smart, playful teenager is replaced by this malicious person. via /r/Parenting http://ift.tt/2vX4HBY