America is a real-world location that is referenced in My Immortal.
In Chapter Twelve's author's note, it is said a lot of Amerikan skoolz are like Hogwarts and have pedophile teachers. Tara included these themes in My Immortal because she "wunted 2 adres da ishu".
We can probably assume Tara and Raven hail from the United States, due to their American influences in their various fanfics. Chains like Hot Topic etc are mentioned often, but Hot Topic has no UK branches (though cell phones are occasionally referred to as "mobiles"). In I'm Not Okay, Eternity supposedly attended Los Angeles High School before running away to Hogwarts (which is in a different country across the ocean).