Oh the tweens

Here I am .. a mom to a 12 yr old who thinks she is 30.. but acts like she is 8. We have our good days and our bad days. Lately seems to be more bad then good.... but I have faith that at some point it will be the other way around. She lies, she is sneaky and is caving in to peer pressure and I am trying my best to guide her the right way. But how am I suppose to compete with boys and friends? And not to mention all the other things that she is exposed to? I stick to my word when I punish her.. I take things from her.. I talk to her but still nothing seems to be getting through. Where oh where has my sweet little girl gone??