It could be a mere coincidence--there are so many people on Earth and so many events that something "like this" (whatever "like this" means) is bound to happen, one could reason. On the other hand, you have to consider the likelihood that you would have heard of a coincidence of that level, the likelihood of all the other coincidences that happen, etc. And there's no way to quantify those things formally/objectively.

Whether or not it happens to be within the parameters of likely coincidence, it could have been her three children reincarnated, or some other form of cosmic grace giving her back what she lost. The worldview of those who assume that it can only have been a mere meaningless coincidence is so fundamentally broken that they can barely even live and breathe under such a flattened, dismal, nonliving mentality.

I googled this and it looks like they used in vitro and aimed to fertilize three eggs. So I mean, that's not a coincidence, and it's a miracle in the sense that modern medicine is a miracle for people who can afford these things, I guess. Personally, I don't really understand how someone can experience horrifying loss on a massive scale and say, "someone's watching over us" because something else they feel good about happens to them. If it were me, I'd be like, hey maybe if god wanted to watch over me he could have prevented the untimely deaths of ALL my children. But whatever, it's not me so what do I know and where do I get off. I'm absolutely glad they feel good about it, and I would never say this TO a person who just had a baby after they lost a child and thought it was a miracle.