The Ghosts at Pemberley by Fenella J. Miller

Kitty Bennet travels to Pemberley to live with the Darcys and become a companion to Miss Georgiana - but her happy days at the grand stately home are soon overshadowed by the unexpected appearance of the spectral inhabitants of the ancient east wing. Their evil purpose becomes all too evident as a series of attacks ensues, with Kitty seemingly their favourite victim. And when they reveal to her the only condition upon which they will leave, she is horrified. Pemberley will have to be permanently abandoned, the Darcy family and their friends and servants fleeing for their very lives - unless the ghosts' thirst for revenge is satisfied...