This is a tough one. I agree with other hubbers that everyone's life would be easier with consistent parenting (by that I mean your husband supporting you).
It sounds like to your daughter, negative attention is better than no attention at all.
Have you tried going straight to your son when she hits him and lavishing attention on him and ignoring her behaviour completely?
If you reflect, is there a chance that through your daughter's eyes you do favour your son at all? ie if he annoys her, do you make excuses for him because he's younger? What happens if you say something like 'yes, I can see he's annoying you. Why don't I take him over here to play and you take the chance to escape or do something else?'
I know that it's ludicrous for her to suggest that you don't love her, but she may really believe that. Have you sat with her and been really open to listening to her reasons why she thinks that? If she can't come up with any, chances are she knows it's a way to get a response out of you.
As for the police thing, I'd turn it into an opportunity to tell her about Kid's Helpline - put the number on the fridge and show her where it is. I don't believe she ever would do that, and if she did she wouldn't do it more than once.
Your husband needs to get on your side. I agree, maybe approaching it as for your daughter's sake might get more out of him. She needs to see him treat you with respect and back you.
You could also ask her teacher what her behaviour is like at school and they can also access support services for you if you need.
I know you're having a rough time at the moment. I hope it picks up.