I think maybe time. Its still very raw for her.
In all honesty I think if my Mum/Nana was burgled in the night I would have nightmares about it. So I sympathise with your daughter.
Talking about it will help. Don't dismiss what she is saying. Saying "but look, you are safe because we do x, y and z" is not going to help her if she doesn't feel safe.
How is your Mum coping? If she's a solid and together as you seem to be then maybe get your Mum to talk to DD about ways that she feels safe - what the police have done to keep her safe, what changes she has made to feel safe, in what ways they make her feel safe.
Don't have the chat with your Mum is she is still nervy though, it could make your DD worse.
Talk to your daughter about things she/you could do that would help her to feel safe. Empower her to tell you, rather than you telling her. Make suggestions, but have it as a two-way conversation.
Talk about the way the mind works aswell. That horrible thoughts are called intrusive and that rather than get rid of them, most people try to block them out by distraction. Teach her some distraction techniques. Give her a million different things she could think about if these thoughts enter her mind (name foods beginning with C, how many different colours can you name, recite your times tables, think about the time when X, Y, Z happened)
- Acknowledge her fears as real
- Empathise and be sympathetic that she is scared.
- Help her verbalise and be reminded in what ways she is safe
- Tell her that the thoughts can just be ignored. Blanked out.
- Teach her how to distract herself
Then, just give her some time.