I would tell her. I had a mc in August 05 and fell again in October 2005. My SIL who I'm very close with fell in December 05 and lost in December 05. She didn't tell me that she fell or lost as it was only 5 days between her finding out and being told that she lost. I felt upset that she didn't tell me. She said that she didn't want to upset me as I was just 12 weeks along when she lost.

Moral of my story - tell her otherwise she might be upset with you for not saying - not because you are pregnant. Good Luck!!