What am I?

I don't know what I am.

I was just one once,

A bubbly child, playing with her thoughts.

But then another entity entered,

A vain girl, concerned with her appearance. 

And yet another joined the pair,

An insecure teenager, worried about her place. 

These three fought.

And out of the wreckage of the battle climbed another,

A broken woman, controlled by her doubts. 

These four now reside, leaving me to wonder:

What am I?