Aw, I'm so sorry you are in this spot because I know this feeling all too well myself :-(
One of my best friends has been TTC for many months and once DH and I started TTC, we were definitely sharing every bit of the journey together. The day before I took my test, I was around all of my friends at my BFF's wedding. I wasn't
feeling too well, and because my friend is charting and knows all the signs, she guessed that I was probably pregnant. Of course, I took a test the next day and got my BFP. She didn't ask me about it for several more weeks, and I didn't share it.
Mostly out of respect for her process and the fact that it was the holidays, etc. I shared it with her a few weeks after the fact, and she was extremely supportive and gracious (as I knew she would be). It's still so hard, though. I would give anything
to be sharing the journey together and hope so much that it will happen for them soon.
I think, like Laurie said, once you reach a certain point where you are comfortable telling people (first u/s, after first trimester, etc.), you could share it with her at that time. It would probably be best if she heard it from you early on
and had time to process it before others find out.
It is so incredibly hard keeping such happy news to yourself in those first few days and weeks. {Hugs}