Mother cat attacking her kittens

[plebayo]

she was put down two days ago, took her to the vet, she was very ill, nothing we could do

Maybe if you had taken her in sooner you could of. It sounds like it could have been a pyometria, which if caught early enough on can be taken care of by spaying the animal and removing the infected uterus. Good on you for getting the kittens spayed so they don't end up having the same issue.