M.C.
I would wait until after the 3m (1st trimester) to tell anyone. The emotions will be raw for her, but it won't be as difficult as if you were pregnant at the same time. I would also call her and let her know before a public announcement.
Also, if she happens to NOT get pregnant again before you do/deliver. Please be mindful of her feelings. Let her be as open or withdrawn as she needs to be. A cousin had a baby just before I miscarried. We then had a family reunion. The baby was about 2m old. Everyone was focused on the baby, but I just wasn't ready, and stayed to myself watching after the older ones. Someone then can over and asked 'why haven't you held the baby yet?'. I responded with 'I am happy for them, but I can't. Please don't ask again'.
Good luck.
M.