Have I failed...

I have recently discovered that my daughter has been having some issues with her father's girlfriend. It is at the point to where she has retaliated in a "parent trap" kind of way. I went out last Friday night to Happy Hour with my girls and I receive a phone call from Taylor laughing and she proceeds to tell me that she hates her Dad's girlfriend and that last week her and her friend cleaned the toilet bowl with her toothbrush, put glue in her deodorant and spilled a bottle of perfume in the bottom of her purse and that she wasn't even close to being done with her! I was mortified and said to her that I was going to pretend that she didn't just call me with that information and that I would talk to her when I got home. When I got off the phone I told the girls what Taylor claimed to have done and they had the same look on their face that I am sure I had (complete disbelief)! When I got home I really didn't even have to really try to get the information out of her, she openly talked about it even in front of the girls. I don't think that even now after the punishment has been handed down that she realizes the damage that she caused. SO I thought about what Taylor had disclosed to me and decided that I should tell her father what she had done, I mean what if the girlfriend got sick and with no punishment and the fact that she said that she wasn't finished with her scared me terribly! I mean she gets mad at me and what would she do to me if she got mad enough? The worst part of the whole thing is that this little girl, my little girl has plotted for revenge against someone! Where did I go wrong? I no longer look at her the same way I did a week ago and that kills me! Her dad and I spoke with her and she told him that she hates her because she always yells at her and is mean to her. Of course he defended the girlfriend and denied that she is ever anything but nice to her. Then out of nowhere Taylor pulled her dad's own card on him! She said to him, why is it ok for you and not ok for me? He looked completely puzzled and asked Taylor what she meant and she looked at him and said, you bag on her all the time when she is not around so why is it ok that you can say stuff about her and I cannot feel that way? Of course he totally denied ever saying anything even though I myself have been subjected to him talking badly about her. He made her tell the girlfriend what she did to her and apologize, and of course the girlfriend yelled at Taylor and now refuses to be anywhere even in a room alone with Taylor. It has been two days since I told her dad and Taylor told me tonight that she still doesn't understand why she id in so much trouble and that what she did wasn't so bad! SO I ask the question to myself again, have I failed?