Brightwood by Tania Unsworth

Summary from Goodreads:

Daisy Fitzjohn knows there are two worlds: the outside world and the world of Brightwood Hall, her home–and the only place she’s ever been. Daisy and her mother have everything they need within its magnificent, half-ruined walls. They may not have a computer or phone, but Daisy has all the friends she could want, including a mischievous talking rat named Tar and the ghostly presence of a long-ago explorer who calls herself Frank.
When Daisy’s mother leaves one morning, a strange visitor arrives on the estate, claiming to be a distant cousin, James Gritting. But as the days tick by and Daisy’s mother doesn’t return, Gritting becomes more and more menacing. He wants Brightwood for himself, and he will do anything to get it, unless Daisy, with only her imaginary companions to help her, can stop him.

Confession:

In some ways this was a very interesting and unique story, but it was also a typical kid left on their own and needing to survive story as well.  Daisy is not your typical ten year old.  She has never left her house and only has her mother to talk to and learn about the world from.  Therefore she is very independent but also has rich imaginary world which at times becomes blurred with her own.  It is her imaginary world which helps her survive in the end, giving her courage to face her fears and figure out how to survive against all odds.

It is a solid middle grade book that I would recommend to kids who like a little bit of the magical mixed in with their realism.