I have four DCs and I think a great deal of this is luck.
My eldest two (DS now 22 and DD now 18) had their moments as teenagers, but nothing that I couldn't handle.
DD2 (now 14), on the other hand, was truly awful. At 12, she was a sweet little primary school child - hardworking, chair of School Council, nice little friends who came to tea and danced to High School Musical.
Six mths later, and at secondary school, she was rude, bitchy, catty, argumentative. Sneaking out of the house in the middle of the night. Hanging out (and having sex with) older boys. Underage drinking and smoking. Shoplifting. Cannabis. Found out my PIN number and stole £500. Got kicked out of school for repeated fighting and swearing at teachers. I am not making this up.
There are no magic answers. I cried buckets, went to the GP for stress, and begged social services for help. They offered me a place on a parenting course (which was useless - designed for parents who needed basic help - eg: don't put coke in your baby's bottle or let your 3 yr old watch snuff movies).
The most useful thing I did was to get her some contraception (an implant - v. reliable, tho doesn't protect against STIs).
Eventually (after about 12 mths) she just grew up. She's still a pain at times, but the stealing, drugs and drinking have stopped. Her tantrums are much less. She's back in mainstream school, and has a really nice set of friends.
Adolescence hits some children really hard. Girls can be dreadfully nasty. Don't beat yourself up about it. Keep repeating "And this will pass". Grit your teeth when others boast about their perfect children.