If you don't want to hurt her feelings then stop talking to her gradually. Go from every day to every other day, then every third day. Then once a week, and so on. Do this till you don't talk to her anymore. The problem is that you work together so you have to be in contact.
I had a friend who I wanted to stop hanging out with. Before I got to gradually stop seeing him we got in a fight and I ended it cold. It really hurt his feelings, which wasn't what I wanted. Slowing pulling away would have been better.