Sabo, I'm so sorry to hear about your friend. It sounds like she has a great friend and support system in you. You seem very sensitive to her needs and feelings.
I was in a similar situation last March, only I was in your friend's shoes. One of my close friends in my playgroup found out she was pregnant right after I did. I had already announced my pregnancy, but she had not. Our playgroup was scheduled to go out one evening for a going-away party for one of our girlfriends. Two days before I ended up having a m/c. She was kind enough to let me know she was pg before she announced it to the rest of the group, kind of to give me time to process it. However, she did choose to announce he pg at our dinner. I didn't begrudge her for it, I knew she was really excited and wanted to share her news when we were all together, but at the same time it was extremely painful for me. I felt obligated to pretend like everything was fine and be really happy and excited for her in front of everyone, when inside all I wanted to do was scream and cry. I think the worst part was that no one took the time to pull me aside and ask how I was doing (they all knew about the m/c). I got home that night and had a horrible breakdown.
I say all this just to let you know that if your friend goes, she would probably really appreciate you keeping your wonderful news in a little longer, if possible. If that isn't feasible, or if someone blows your cover (my friends would be all over me if I didn't have a drink!), I think just taking a private moment to let her know you're thinking of her and asking her how she's doing could mean a lot to her. I didn't necessarily want my friends falling all over me with sympathy, especially at a party, but just a simple acknowledgment that I might be in pain would have meant so much.
Let us know how it goes.