I can't tell anyone my best friend is preggo
What do you think will happen if you tell someone?
I know that she'll be mad at me if I tell anyone.
It's understandable that you wouldn't want to give away your best friend's secret. You should always support your friends when they are going through a tough time. Your friend will reveal her pregnancy when she feels it is best to do so.
Well, I think she shouldn't do it at work, she should be excited and looking forward to it.
When people are pregnant, they often wait a long time to tell people. So if you were to share that information, you'd be betraying her trust. You should feel honored that she told you so early and then wait until she's ready.