Kisa Gotami lived during the same time as the Buddha, i.e., around 500 BCE.
When her son died, she was terribly distraught, and saught out the Buddha, asking him to bring her son back to life.
Could the Buddha have done it? Perhaps, I don't know. But the Buddha, unlike the founder a certain other popular religion refused to perform miracles as he viewed them as hindrances to spiritual maturity.
So, the only right thing to do, as far as he was concerned was to teach her that death is part of life. But Kisa Gotami was not in the mood to listen to explanations about the nature of life. After all, she was filled with grief.
The Buddha understood that fully. So, instead of talking to her, he asked her to go and get a handful of mustard seeds from a person who had never lost a dear one through death.
Kisa Gotami went from house to house in search of those mustard seeds. Seeing she was mourning the death of her son, everyone was quite compassionate with her, and willing to give as many mustard seeds as she wanted. Alas, no one she met had never lost a dear one through death.
Gradually, Kisa Gotami came to the realization that death is a natural occurrence, a part of life to be experienced by any being that is born. Once she accepted that, she returned to the Buddha and thanked him for showing her the truth about death.