Where Oh Where Has My Darling Daughter Gone?

Help! My darling daughter, Twelve, is possessed. Shocking you might say, after all this is the same dd who used to think that I was the "best mommy in the world". True, that was a looooooong time ago, but nonetheless, she used to like me. Now, I believe aliens have taken her and slowly replaced her once sweet disposition with a "mom you don't know anything" replacement. She screeches, she rolls her eyes, she whines. I keep "thinking, wishing, hoping, praying" (hey isn't that from a song?) that this is just a phase that she is going through. Now I'm getting worried that this so-called phase is never going to end. In fact, just when I think that she is as "possessed" as she is ever going to be, she "kicks it up a notch" , "lets it all out" and becomes even more annoying. Then when I feel that I am at the end of my rope and ready to snap, she miraculously is able to completely pull it together and be the sweet dd that I used to know (of course this is usually because she wants something from me!). I'm stressed...I'm feeling like a failure as a mom...I feel like somehow it's all my fault. I still love my daughter, but I can't say I like her very much right now. In the meantime, I 'm continuing to give Amber, the dog, her double dose of sedatives (and it seems to be working)...I wonder if she would share with me...not for too long...just until I get my darling daughter back.