You cannot have a civilised society when people take justice into their own hands.
Apart from that, I have no particular sympathy for him, but she deprived her children of a mother for 4 years, which is not on.
It’s a terrible thing to suffer as a parent, but what she did was selfish, giving her to her (totally understandable) desire for vengeance, rather than putting her children’s welfare first - especially awful given the trauma they’d experienced.
I am sure her kids love her, hence the expressions of support, but they will have been damaged by her as well as him, and when they are older they will realise that.