I don't know what the outcome will be. Maybe she'll live to be 100. Maybe the hired nurse will be a good "substitute mother" for many years. Maybe the child will be happy. We can't predict the future, which is why morality can't be based on outcome.
Perhaps she could have dealt with her guilt by allowing this child (which is not genetically hers, after all) to be adopted by a married couple. Although that wouldn't help the (at least three) babies who died during the "production" of the one that survived.
My parents were 40 when I was born. I have an "old" family; everyone was and is OLD. While my parents were wonderful and they outlived many of my friends' parents, there is a generational mindset gap. Despite older parents congratulating themselves about how their kids "keep them young" imo there is just something missing for the kids.