What's the Name of That Book??? discussion

Looking for a book I read years ago. It couldn't have been published any later than 2012. I believe it is a children's mystery/fantasy chapter book. I think the cover had a forest on it and an iron gate.
As for the plot it followed a girl (penny I think) who moved to a small town with her mother to work at an old manor that is owned and lived in by a rich family. There's a boy (blonde I think) who either works there in the kitchen or is a member of the actual rich family. There are certain rooms Penny can't go in either. the manor is surrounded by a forest, where magical creatures live. Witches and/or fairies. I can't remember which. There's a mystery in the forest. Girls went missing in their long ago I think. One of them was a raven-haired girl who is actually the villain I believe. There's a specific part of the book that I remember: Penny breaks into an old man's room (member of the rich family) it's revealed he used to date the raven-haired girl and has gone made since she disappeared. he keeps a lock of her hair under his pillow and Penny has to rip it out of his hands and he screams and cries. He calls out for her. I think the raven-haired girl dies in the end? This is all I can remember. Please help, I've been searching for such a long time.

Some plot points match The Mysterious Howling

Sarah, please add plot details to your header to make it easier for the people searching for your book. This is helpful both before and after the query has been solved. (A lot of old queries help solve new queries.)

I've actually found the book
it's 13 treasures by Michelle Harrison.

Glad you found your book. Here's the link - 13 Treasures by Michelle Harrison. I added a description to the topic header which might help people searching for this book in the future.