Danny Phantom Theory 1: Ember's Song explains her backstory and how she died.

Yeah! Oh!

It was, it was September

Winds blow, the dead leaves fall

To you, I did surrender

Two weeks, you didn't call

Your life goes on without me

My life, a losing game

But you should, you should not doubt me

You will remember my name

Oh, Ember, you will remember

Ember, one thing remains

Oh, Ember, so warm and tender

You will remember my name

Your heart, your heart has rendered

Your loss, now bear the shame.

Like dead trees, in cold December

Nothing but ashes remain

Oh, Ember, you will remember

Ember, one thing remains

Ember, so warm and tender

You will remember my name

Oh, woah, woah!

Ember, you will remember

Ember, one thing remains

Ember, so warm and tender

You will remember my name

Yeah! You will remember my name

So could the song talk about how Ember was in love with this dude and they had the common 5 dates then he move on and she waited for him but he never came back. This cause her to not only make this

song but take on a more punk look to show her heart was broken. But lets say she made some songs

that made her some what famous and her old lover came back to her cause she was becoming popular/

They went back being a couple and then Ember then started to loose fans to due her recent songs and this would have the dude leave again and cheated on Ember with another teen singer and this cause Ember to break and she ran off into the woods, but in the song it says 

"Your loss, now bear the shame.

Like dead trees, in cold December

Nothing but ashes remain"

This could mean 2 outcomes for Ember. For one she could of froze to death. What I mean by this

is that she ran into the woods and cried while leaning on a tree and it began to snow and since she was in her performance outfit she most likely froze to death.

My Second idea was that she lit her home on fire and sat in the burning house ready for death.

This could be why in her ghost form she has Blue Fire for hair.

Maybe someday or some way we'll find about the origins of the ghost within Danny Phantom.

Here are some Vids I found that could help the theory, also here's the music video for Ember.