You're right a FEW were rational, most exhibited a disgusting level of selfishness.
These children that she left behind have an amazing mother. I can't imagine knowing that my life was soon going to end and that I would miss my children growing up. However, if I had cancer and was going to die before long anyway, I like to think that I would make a similar decision. What better gift to the existing children than another sibling to grow with. A this last child will always know how much his/her mother loved him.
It's sad that things like this have to happen. We all weep for their loss.