I think that this woman has an intense liking of you and has extreme insecurities, which is why she gets mad when you say "its whatever" or "I don't care" because she's insecure. This is probably one of those examples of why office romances are a bad idea. I think you should just leave her alone.
Tell her you're not interested in a relationship, but in a nice way and for kindness offer to be friends, just friends. Because otherwise I think she's going to make your work life miserable and keep saying things. If the friends offer doesn't work, just let her be and leave her alone.
Hope this helps! :)