Play cold or explain how I feel

I met this girl over the summer at a casual job and developed feelings although I knew she had a boyfriend (on and off for about 2 years) After summer the job ends and we start talking more and it becomes flirting and I find out she no longer has a boyfriend so we decide to go out and on the date I find out that they broke up because he cheated on her. Date goes well and we both want to see each other again so we go out again and have a wonderful time. She is hosting a party the next day and mentions if there is mostly couples there she would love to invite me. I don't hear from her the next day so I assume some single friends came and they all had a good time. The day after that I get a text from her out of the blue saying "I just wanted to let you know that I'm back with my boyfriend" then said she didn't want to lead me on. Now, we do work together on Saturday (summer job is now causal weekends) so I am trying to decide if I should ignore/ give her the cold shoulder this would not affect our jobs as we don't work together but at the same place or if I should be friendly/ let her know how I feel as I do have feelings for her still and I feel a bit hurt? sorry for the long write up and let me know if anything doesn't make sence.