Should I go to her birthday lunch ? Really need some advice.....

My co-worker (I'll call her Miss A) and I been working in the same dept. for a long time. We get along ok all these years and I consider her a friend at work. We go out for our birthday lunch, have coffee together on our breaks occasionally etc.

Few months ago, she made a "very offensive" comment about me. I was very upset and offended by that. I was hurt becuase I felt that she has betrayed me. Few days later, she apologized to me and I accepted her apologies because we work in the same dept. and see each other everyday. I don't like to have conflict at work place.

Since the incident, I've been keeping a distant from her, I don't talk to her unless she initiates the conversation. Otherwise, I just talk to her relating to work only.

Anyway, make the long story short, her birthday is coming up soon. My other co-worker (whom I also friend with) asked me about taking "Miss A" out for her birthday lunch. I haven't answered her yet. But I don't feel like going, I feel that my friendship with "Miss A" have drifted apart since that time. I hate to say that but I don't think I like to be friend with her anymore. I now only consider her as another colleague at work.

I need some advice as to whether or not I should go to her birthday lunch. If I go, I would feel awkward and I don't want to be so fake. But if I don't go, what excuses can I use or say so that I will not upset anyone ? I know she will not be happy and will start talking to other people about it. She is a very sensitive person. Any advices I can get would be much appreciated. Thank you.