She did say she got stuck as a gyaru in the temporary prison, but that doesn't explain why that version of isabelle would be in Erica's mind, especially if Erica hadn't even been to the prison yet for that to be planted in his brain. It's highly doubtful that Wendy would have had access to Isabelle's old transformation kit and that it would have put Gyaru isabelle in his mind, especially since she was inside of his sealed memories. My theory is that everything inside of the seal was a fractured version of what it used to be, hence the destroyed Earth, burning campsite, and possibly even Shelly/Phyre's broken mind. Gyaru isabelle is a version of isabelle that is fractured which is concealing the truth. There are other possibilities as to why she would be like this, but this is the most satisfying conclusion in my mind.