When You Get the Chance by Emma Lord

Nothing will get in the way of Millie Price's dream of becoming a Broadway star. Not her lovable but super introverted dad, who raised Millie alone since she was a baby or her drama club rival, Oliver, who is the very definition of Simmering Romantic Tension. Millie needs an ally. And when an accidentally left-open browser brings Millie to her dad's embarrassingly moody LiveJournal from 2003, Millie knows just what to do - find her mum.
But how can you find a new part of your life and expect it to fit into your old one without leaving any marks? And why is it that when you go looking for the past, it somehow keeps bringing you back to what you've had all along?