Ngaiol, I'm so sorry you're going through this, but I'm glad you listened to the professionals. As a PP said, it's not just about protecting DD, but also about protecting you. Also, if they're not allowed to be at each other's flats, I assume the police don't want them together, period. Letting them get around that by moving in w/ you, would be defying the police in my view. Good that you decided not to.
Glad you changed the locks, too! I would even be wary of letting DD stay at my house for more than a few hours' visit, if that, b/c she might bring him in after a while. I know you love her and might want to see her sometimes, but IMO, that would be better at a neutral place, neither her house or yours.
In time, I hope, DD will realize this man is not for her. Unfortunately, it's not uncommon for young women to have to experience a few bad episodes before they come to this realization. I trust you will be there for her when she does, no matter how long it takes. Until then, please be patient - and careful. Hugs!