Title: Fatal Secrets
Author: Richie Tankersley Cusick
Published: November 17, 1995
Publisher: Scholastic Point
When Marissa falls to her icy death, her sister Ryan believes she could have done more to save her. If only she'd got there quicker, if only they hadn't argued, if only she'd listened. Because Marissa had a secret that was scaring her to death. And now that secret is haunting Ryan. (fantasticfiction.co.uk)
How horrifyingly ambiguous! I'm not sure what the demon dead dolls have anything to do with this but I'm already not going to sleep tonight. That horse giving me the stink eye isn't helping either.