Am in a similar situation, posted once an issue with this workmate. I'm the engineer, and she's the architect. Have to see her every 2 weeks on a constant basis, for at least 5 years. Really sucks. Kailex or the rest of the other posters would tell you NEVER even have thoughts with someone you work with.
I learned it the hard way, and still am. I paid the price, now its ugly. So if you want something else than just ignoring her, how bout keep things real professional. Set in mind PROFESSIONALISM comes first and like Robert28 says, keep things short. Trust me, you don't want to get involved with a person from work. Nowadays, i just tell her what she wants in regards to the project and that's that.