I love Alexandra Potter's writing style, although sometimes the themes of the books are a little unusual. That's the beauty of fiction: it can allow you to escape from the confines of reality - Alexandra does this beautifully, yet fairly believably, in this book.
As I began to read Who's That Girl, I found myself reading too quickly - I'd adapted my reading style to the hyper main character, and the way I envisaged her talking! I found it easy to immerse myself in the book (to the detriment of my college work) and, against my expextations, didn't find the plot completely outlandish.
I don't want to give the story away, but would suggest that you give this book a try. It's easy to read, isn't too deep, and is an enjoyable way to pass some time.