My teen seems like an adult one minute and a little kid the next. Will this ever even out?
Your child's social/emotional behaviors are right on the money. I call teens "man-boys" or "woman-girls." It's as though they are teetering with one foot on either side of the fence. There is a simultaneous increase and decrease in maturity, as they work to define themselves and master the anxiety and insecurities associated with developing her independence. In my opinion, teens are developmentally a lot like toddlers. They are maturing and striving for independence, while at the same time running back to parents' coattails, feeling insecure and unsure of themselves.
Girls tend to demonstrate this more outwardly than boys, by nature of their tendency to exhibit more emotion. Boys may tend to withdraw, procrastinate or take on an air of pseudo-maturity to hide their insecurities. Your daughter is doing exactly what she is supposed to be doing. Allow both the mature and the immature sides to be exhibited. And just remember, as perplexing and frustrating as it may be for you, your daughter is experiencing those emotions tenfold. And this too shall pass.