I think it depends on you, actually, as to how you handle this. Do you want children and does she know that? Are you medically unable to have children, or are you just in a place right now where its not feasible to have children? If she knows that you desire children but CANNOT have them (medically), then she probably is backing away because she feels like she's rubbing your face in the fact that she can be pregnant while you can't. If she thinks that you might get hurt by her sharing all the joyous news in her life while you're going through such a hard time, that could also be why she's backing away.
Personally, I think giving it time is a bad idea. It sounds as if you two don't live in the same city, so a coffee date or girls day isn't an option. Email is not the best way to correspond in situations like this, as it doesn't allow for someone to truly understand how the person on the other end is speaking. Plain text just can't convey true feelings and thoughts. So I would try calling her, and say that you are very excited for her and that you love her, and you feel like there's something coming between you but you aren't sure what it is. Give her the chance to say whether or not she feels that same barrier. If she doesn't, it is entirely possible that she's just gotten busy or is dealing with alot (some women get so sick in the first trimester that doing much of anything is nearly impossible), and isn't intentionally ignoring you. But let her know that you want to be a part of this with her, that even if she's afraid to share something for whatever reason, that you still would like to hear it. I'd even suggest trying to plan a visit together, if at all possible.
Those are just my suggestions, but I hope it helps.