First of all, I advocated exactly what you say at the end. Namely, that the friend with good news should stay involved and be sensitive. She should not avoid that topic, but neither should she flaunt it. It is a difficult balance, but not too difficult, and though she might make a mistake once in a while, a well-adjusted person can deal with the occasional slip by her friend.
Now, to the point of our disagreement: If (and only if) the friend with no children cannot deal with the friend who has children (assuming that friend is sensitive as I described above), then whose problem is that, I ask you? The person with painful emotions is the only person who can repair the pain. And that doesn’t have to mean therapy. It can mean anything that helps her stay in control and not lose her friend.