Fading Starlight by Kathryn Cushman. The book is being released by Bethany House on May 3, 2016.
Amazon says this about the book: Lauren Summers is hiding. Her fashion house internship should have launched her career, but a red carpet accident has left her blackballed. The only job she finds is unpaid, but comes with free lodging--a run-down cottage in the shadow of a cliff-side mansion. Unsure of what comes next, she's surprised to be contacted by a reporter researching a reclusive former Hollywood ingénue who lives in the nearby mansion.
Kendall Joiner wants Lauren's help uncovering the old woman's secrets. In return, she'll prove the red carpet accident was a publicity stunt so Lauren can regain her former job. With all her dreams in front of her, Lauren's tempted by the offer, but as she and the old woman get to know each other, Lauren realizes nothing is quite as it seems.