Mexican Gothic

At first I thought this book was annoying, but then I thought it was incredible. It reads like YA sometimes, and the protagonist feels out of place for the time period the story is set in, but I did enjoy this book overall. An English family sets up residence in Mexico and strips the land of precious minerals, building an estate in the mountains. The protagonist comes to the estate to rescue her cousin, who married into this family and has been writing increasingly strange letters.