After reading the story, I believe it said she found out she was pregnant first, then some time later found out that she had cancer.
As someone that has gone thru this same situation, but reversed, it is no ones business except the mom, dad and the physicians. My wife and I weighed all the options, spoke to numerous high risk OB's and hematologists before a decision was made to proceed with chemo. In our case, it was 50/50 if the chemo would affect the pregnancy, however, the cancer was definitely going to affect the pregnancy.
I commend her for the decision that she made. The child will be fine. There will be loving parents, she can be told when she is ready what happened. It is not like you are going to spring it on her at her 5th birthday party.