Twenties Girl by Sophie Kinsella
Lara has always had an overactive imagination. Now she wonders if she is losing her mind. Normal twenty-something girls just don't get visited by ghosts! But inexplicably, the spirit of Lara's great aunt Sadie - in the form of a bold, demanding Charleston-dancing girl - has appeared to make one last request: Lara must track down a missing necklace Sadie simply can't rest without. Lara's got enough problems of her own. Her start-up company is floundering, her best friend and business partner has run off to Goa, and she's just been dumped by the love of her life. But as Lara spends time with Sadie, life becomes more glamorous and their treasure hunt turns into something intriguing and romantic. Could Sadie's ghost be the answer to Lara's problems and can two girls from different times end up learning something special from each other?