Lucille is a very busy, serious student. She is known as an overachiever. Working so hard means, she has to make sacrifices - the kind of things that make you more fun to be around. So Lucille imagines the second version of her will give her more time to do fun things. Her clone can go to school, and no one will ever know the difference.
You've probably already guessed that it doesn't work out the way she hopes it will. Her clone (Lucy) is not a robot. She has feelings and (oddly enough) different interests. Also, the tech company considers Lucy property that it will take back after a month. Ethical dilemmas abound, but for awhile Lucille is only concerned about herself and her new found freedom.
At it's core, this story is about a teen who tries to make her life easier and ends up in a much bigger situation than she imagined. It is livened up with the problems of trying to keep the clone a secret and the related ethical issues. It's best not to get bogged down in the science of creating such a clone and the other plot issues. If you accept the premise as is, then this book is worth your time.
For more info, check out the Indianapolis Public Library catalog and the author's site.