Sisters Under the Skin by Willa Marsh
Stepsisters Olivia and Emily are at daggers drawn - until the arrival of their half-sister, Rosie, when they unite in their hatred of the newcomer. Rosie can certainly look after herself, and cunningly throws secret spanners in the works for her older sisters. But when all three are grown up, and it looks as though Rosie is going to force the other two out of their beloved family home, they decide to put a stop to their sister's antics once and for all.