What I meant was that this particular woman is not the only person who could raise these children. Many children go on to have wonderful loving adoptive parents after the death of their birth parents. By choosing to give her fourth child a chance a life, she is not dooming her other three children to a life without a family.
Sure, they will have family, but they won't have a mother. She chose NOT to mother them. All the adult perspective in the world won't help children to understand why their mother chose to leave them.
Why is the life of the unborn MORE important than the life of the mother? That is what is happening here. People aren't saying, "Both lives are important." The unborn is MORE important and overrides the mother's life PLUS the impact the mother's death would have on the rest of the family.