Yes I thought she was on lock. Julianne's performance was too much Oscar bait and is a role that feels like a been there done that performance (mental illness, how it affects the person's life, how the people around adjust to it, etc. etc).
Rosamund's character was haunting, you love the character even though you hate her too much. She was cold, manipulative and unpredictable and the way she delivers her lines with those terrifying glares and cold voice

The way she transitions from innocent girl to murderous sociopath effortlessly too. She was born for that role