how do I tell my sister who is TTC but not open about it?

Over 2 years ago my sister mentioned that her and her husband were going to start to TTC. Since fertility has been an issue for other members of my family we have been curious how the process has been going but she is very private about the whole thing and I respect that.  I know she has seen a fertility specialist and that's about it. Last time I asked about plans for a baby she said that they are really happy the way their lives are right now but if it happens it happens. And I believe her.  SOOOO... help me decide. Should I announce our (surprise) pregnancy to her with the rest of the family on Easter and not make a deal about it, or do you think she would appreciate a private announcement or note for time to process?