Possible coworker break up what can I do?

I think you're gonna have to let this go, she has made it clear that she is not interested. She is probably saying she isn"t ready for anything because its an easy way to let you down, she may very well like someone else. Lots of women just enjoy being flirty with other men, it makes them feel wanted even if they are not interested in them. Just stop contacting her or she'll really start to feel harrassed and creepped out.