antiabz, full apologies from me if you have interpreted the thread as meaning the children were any less worthy of life for being SEN. I can understand how you read it that way and how upsetting that is.
FWIW I really don't think anyone who has compassion for her thinks this. I just understand how desperate people get when caring, alone, for a very sick child, having done it, and can imagine the pressure of caring for three might leave you feeling so desperate and shattered that you are no longer capable of rational thought. Like Pag, I remember feeling so diminished by DS's illness, so incapable of bringing relief to his perpetual pain, or to be a half good mother to his healthy brother, that I briefly thought they'd all be better off without me around. Such thinking is so out of whack with reality that it helps me to understand how close that is to thinking a child would be better off not in this world.
What she did was wrong. But that is not the same as saying what she did was wicked. That would suggest that she had full capacity to behave in a rational way and a lot of people here feel that in her circumstances we too would have been irrational, however wrong that reaction would be.