M.J. Mallon 
Bloodstone [EPUB ebook] 

Fifteen-year-old Amelina Scott lives in Cambridge with her dysfunctional family, a mysterious black cat, and an unusual girl who is imprisoned within the mirrors located in her house.
When an unexpected message arrives inviting her to visit the Crystal Cottage, she sets off on a forbidden path where she encounters Ryder: a charismatic, perplexing stranger.
With the help of a magical paint set and some crystal wizard stones, can Amelina discover the truth about her family?
A unique, imaginative mystery full of magic-wielding and dark elements, Bloodstone is a riveting adventure for anyone interested in fantasy, mythology or the world of the paranormal.