Is this considered Blackmail? And Is it Illegal?

I just went threw a very rough break up with my girlfriend. After an argument a few weeks ago, she suddenly decided to give me the cold shoulder forever. Ignoring all of my calls and requests to get my property back from her. IE - Laptop, suits , clothing, stuff of mine that was laying around her house. You see, we had an argument at a party. Her sister got involved, and told her to leave me apparently. So I have heard from neutral friends. Well , I contacted the Police and told them that she is not responding or answering my calls to get my property back. They told me to leave her a voice mail saying I'm getting the police involved if she doesn't call me back. So I do so. Then my girlfriend, of 3 years, decides to send me an email saying she will basicly rat me out about things I have told her that I have done at work. Not to say these things are illegal , but basically confidential stuff that , that goes on at every work. She Emailed me saying " oh really, is this about really about ------------------- that you told me you were involved with at work? Is that what this is really about? The fact that I'm aware you did those things, go head get the police involved, I will tell them about you"..... Is that considered blackmail? I mean the things I told her were not unnecessary illegal , but merely unethical things I've had to do here and there to get the job done. So now, basicly, she's threatening to go to the cops and tell them those things about me, Simply because she does not want to, or is unwilling to work with me to get me my things back.