Give Me Five by Meg Cabot (The Princess Diaries #5)

It's nearly Mia's fifteenth birthday. A time when a princess should be getting ready for the biggest night of her life- the Senior Prom, escorted by her ultra-hottie boyfriend, Michael.

 But nothing's going according to plan. Michael hasn't even invited her to the prom yet. Hello, what exactly is going ON there? Just as Mia cooks up a plan to change Michael's mind, disaster strikes. The kind of disaster that only a miracle can overcome. A miracle called Grandmere ...