You'll get a lot of "don't dip your pen in the company ink" replies, but I'm going to explain to you, from first-hand experience, why it's best not to mess with her:
1.) You see her every work day. If something goes wrong (e.g., you develop one-it-is; she turns out to be a psycho; she’s a gossip wh0re and discovers you have a small pecker, etc.) are you prepared to expose yourself to her and her drama on a regular basis?
2.) If you’re the type to get jealous easily or clingy, quit while you’re ahead. One day, you might think she’s into you; the next day, she’ll be going to lunch with another co-worker…possibly screwing him, too. Are you prepared to deal with that? Every hour you’re at work, you’ll be burdened with crazy thoughts like, “Why did she and the new guy leave at the same time? Are they going out and trying to be sneaky about it?”
3.) You won’t be able to focus on work, but she will. Care to know why? Because she knows she has you and probably every other guy at work wrapped around her little finger. Her mind won’t be in turmoil.
I've been there before, and right now, I'm going through some crazy stuff with this one psycho co-worker. I'm in the process of switching jobs.