My brother-in-law's first wife was faced with the same choice: she found out she had cancer not long after she learned she was pregnant. She also refused treatment in an effort to save her baby's life even at the cost of her own. The baby died unborn, two days before she did. She left my brother-in-law with three small children, ages 2 to 6. Thankfully my (future) wife and her parents were able to build a house next door and help out for several years.
"The baby died unborn, two days before she did. "
How sad! Life sometimes deals us hands we can't understand, it seems. I'm so sorry for your brother-in-law. He will need much strength of spirit.
Her action ws, nonetheless, heroic, even though the child died. The way you put it, one thinks that you think she was derelict in her duties.
I hope your brother-in-law is comforted by the fact that his late first wife was a saint and went straight to Heaven.
Thank you for posting such an inspiring story. It seems there are still heroes and heroines in this world.