In my opinion, personifying Emotions and Elements never gets old. Even I have a short ten-minute play in my past where a girl has to face her own Arrogance, Tedium, Morbidity, Fear, Desire, Malice, and finally Hope. Ran at a student playwriting festival back in 2004. One woman came up to me afterward and told me in heartfelt tones that I had described her life.
After all, it's so much easier when you can condense Emotions from something tangled and abstract into a person. You can relate with a person, argue with a person, fall in love with a person. The relationship between Liz and Fear is the major hook of the book, and one that ultimately pays off.
My main issue with this book is pacing. The beginning was perfect, the ending was a little fast, but the middle dragged. Her brother's revelation about the "I'm not Liz" line is great, but needed to happen much sooner, about the same time as her conversation with her mother in the kitchen, when she asks where her daughter is. That would have been an easy transition, if her mother inspired doubts and she went up to ask her brother. And after that it needs to snowball to breaking the block. Instead, we continue to wander through emotional limbo, killing any momentum that might have built up.