Why did she...?

When the cop was guarding/waiting outside her door, why did she unlock the door?

He was sitting there when suddenly he saw the blue LED light and heard the lock open. Admittedly,we didn't see her open it,she was asleep when he entered her bedroom. But if she didn't unlock the door,how did it suddenly become unlocked?

It seemed like she was inviting him in, but obviously, after what ended up happening, she wasn't.