Is expiation obligatory for a woman whose sick infant daughter slept beside her, and then she found her dead in the morning, and she does not know whether the death was due to the illness or due to a blanket the mother placed on her?

We ask Allah for this mother to grant her good solace and compensate her with something better than what she lost. We do not see that she is liable for anything that happened, neither expiation (kaffarah) nor blood money (diyah) nor anything else, unless it is proven that she was a cause in the killing. As for doubt, nothing is entailed by it, because doubt about the cause is null and void.