Am I responsible for my daughter’s death and do I owe expiation, knowing that she suffered from serious health conditions, and I was providing her with continuous care, and I found her deceased a short while after breastfeeding her?

A Muslim must rescue anyone who is in peril, for Allah Almighty says: "And whoever saves a life, it is as though he has saved all mankind." Sin only occurs in rescue if the rescuer is negligent or derelict. If a Muslim exerts his utmost effort in rescue, then no negligence is apparent from him.