I can see this is an emotional time for her. My guess, and that's all it is, would be to err on the side of communication. You could ask her if she wants to talk about how she feels about her sister getting engaged, maybe over a glass of wine. Or, skip the sister, since this is really about your wife and children, and ask if she has thought about trying to have a child again. Even if that means adopting. I know that when my H and I were going through the adoption process, it brought us a lot closer together. We were on the same team, working towards the same goal.
