I think when a mother sees her children in pain - physically or emotionally - it's an automatic reaction to find the cause and blame someone.
To be fair, I've just been watching a news report where she's been talking about this, and it doesn't seem that she is blaming the school. Rather, she is suggesting that there should be better policies in place in schools, i.e. two contact numbers, not one, and home visits if they get no reply from either number.
It was a terrible tragedy and those poor little girls have not only the tragedy of losing their father, but the trauma of having spent the night, all day, and the evening in bed with his body, too scared to go downstairs by themselves. My heart breaks for them and their mother.