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.