She died in a house fire, not in a concert.

"According to one of the creators for the show, before she died, Ember was an unpopular high school-aged girl who had large dreams of becoming a rock star. One day a boy asked her out to the movies. She waited all night for him to show up, saying, "He's just running late." When morning came and he didn't show up, Ember went home. She was so exhausted that she fell asleep and didn't wake up when her house mysteriously caught fire. She died in the flames,"

Two be fair, ALL of the ghost died, Which is pretty fucked up for a kids show.