Yup, I had a daycare family that never once said a word. Not during the interview (she would have been in her first tri, though, so okay), not for the next 4 months. Their son spilled the beans and I finally said "So I hear that congratulations are in order? How wonderful!" This was also a family that had BRUTAL communication skills, so no surprise.
I also think that you should say "So-and-so keeps mentioning her "baby". Do you have great news?" BIG happy grin.
I think people feel like we are going to be so mad. To me, it's just part of the business. When I get a one year old, and he/she is the first baby. I really only anticipate to have them one or two years tops, before baby #2 comes along. Just how it is!
Perhaps she hasn't said anything because she isn't really a "planner". So she doesn't figure it's going to impact you until fall anyway.
I do think it's odd, but more so because I am also the type of person who spills the beans as soon as the egg is fertilized. LoL