Do i have to inform someone that im going to sue them before i take any firther action?

I'm going to sue a girl at my job for libel and slander. She falsely accused me of stealing her car keys and then messing with her car. I clearly didn't mess with it just because I rather focus on my job than other things. When this incident happened she called the cops and all of her friends. Just before that she had confronted my sister and said it was me. Even though I was home already. I left my house to go speak to her and the police officer that I didn't have anything to do it. She said that she thought it was me because I am the person that least likes, and all of her friends said it was me as well because of that. I thought the problem was over after we made things clear, she now is still accusing me that it was still me and I somehow was wearing gloves while doing the action. I don't understand why she's doing all of this. I know its just affecting me, and I just want to everything end.