If her husband had been ill for a long time, it is likely that she was living a very stressful life for a long time. It is hard to watch – and care for – anyone close to you who is suffering and slowly, inevitably dying. For pretty much all people in this situation, the death of the loved one who has endured prolonged suffering does come as a relief. For some, feeling relief means feeling guilt. "If I loved him it is wrong to feel relieved that he is dead".
One of my beloved aunts, who more or less single-handedly until nearly the end and unbelievably cheerfully and delightfully – nursed her husband while brain cancer reduced him, told me at the funeral, "I did the crying when he did the suffering. The suffering is ended and so is the crying." She must have missed him terribly but she never felt guilty that both he and she were, in their different ways, relieved.
Others may not be so wise.