It is very nice of you, the way you want to be supportive and be there for your friend. Not many friends recognize that it is a struggle going through this phase.
I would say the same thing as Jesridge above suggested. Definately make time to spend with her without the kids and without kid talk at times, just to enjoy each others company. I guess if you are around when they ask her that question, maybe you can change the topic from who started it

that helps a lot

All the best to your friendship, wish I had supportive friends like you.