Have to be honest, I took drugs - ecstasy and cocaine from the age of 14 until 20, that also had something to do with the mood swings. I think you definitely need to see if drugs could be influencing her. Got in with the wrong crowd as such but even before I started all that, I was getting bad with attitude, school etc. I was expelled and had to have a Home Tutor. I had a total disregard for authority. As a baby and child in primary I was practically an angel. As I view it I always feel that some children don't like being babies or toddlers and play up and some children don't like being teenagers and act in a way like a toddler. Like all children have a period where they test their parents and their love for them. A form of attention in a way.
My relationship with my parents now is absolutely 200% WONDERFUL. They stood by me, didn't pressure me too much and sort of realised that I would grow out of it (helped that my dad had been a teacher and studied psychology so had a better grasp of behaviour than most parents). There wasn't an awful lot they could do to be honest. It makes me very very sad now but do you know what, it made me the person I am and it has made me realise what fabulous parents I have. What doesn't break you makes you stronger.
My advice to you would be to be as FIRM as you can be. Take absolutely no shit from her. Take all privileges away the moment she steps out of line. You have to have ZERO tolerance. As awful as it sounds, one day, after a monumental tantrum from me, my dad flipped and laid into me. As wrong as it was, it made me stand up and realise that I had pushed too far.
Do you mind if I ask what type of parent you are? Are you leaning towards being a bit too soft? My mum was and I walked all over her. My dad was very very very busy with his career and I felt that he didn't care.
Please stay strong, you will laugh about it in years to come. We do.
I dread my DDs becoming teenagers though.