How should I treat my (unfaithful) ex gf?

So I broke up with my gf of 6 months after I found out she was unfaithful with me with her ex bf. While we were dating I suspected something was up with her but she always just denied it saying "I would never go back to him" and "I am so over him." A while back, We talked about infidelity and she swore that she was so against cheating and she repeatedly warned me to never cheat on her. Well, I caught her with her ex (he spent the night at her house) last week and I promptly dropped kick her from my life. To make matters worse, she lied to my face the next morning regarding the incident; she also seemed more worried about her reputation from now on than trying to apologize to me. I am most bothered by the lying. I feel so disrespected that I don't even think I can look at her from now on. Too bad, we were good friends before we dated but her betrayal really rocked me. Unfortunately, we live in a small town and work at the same place. Aaargh. How should I treat her from now on?