HI hun I was in a similar situation with my pregnancy before Jake.... and I worked with my friend too. She was trying to avoid me bcos she didn't want to upset me w her growing bump and we both didn't know how to handle the situation. Finally we sat down had a chat and cry about it and I told her excatly what you said in your OP:
I feel confused, angry and empty. Angry with myself because i denied the fact that I pregnant for so long. Angry with the world because its not fair to give something so precious and then take it away. I still want to be a part of her experience, even though there will be times where I can't bare it
If she is a friend she will understand that you will struggle but you still want to be there for her, and as long as she understands why you may be a little distant a times, you will come out the other side stronger as friends and you won't miss out on sharing such a wonderful experience with your best friend.