What should I do about a nosy co-worker?

A lady I work with is driving me crazy. Every time someone come to speak to me she runs over to my cubicle and just satnds there listening. A couple of times she has even elbowed her way into my cubicle and stood between me and the person I was talking to. When she comes to speak to me when I’m by myself she invades my personal space. She will satnd about 3 inches away from me. I have asked her to back up and she gets a little pissy about it. I don’t to start a big argument with her because we are at work. How do I tell her to leave me alone without causing drama?