My step daughter busted my kids face with a stick

While playing on the beach my step daughter smacked my kid with a stick and cut his eyebrow open. 

And no this was not the first time she hits him just for the fun of it. 

He's 9 she's 6. 

I did tell him he's allowed to hit her back if she hosts him but he says he not supposed to hit girls (yeah I taught him that right) 

And I'm also the same lady that made the post a few months ago about her having sexual behaviors towards my kid and putting a pillow over my 4 month old baby while she was asleep (but all the bitches were too busy being mad cause I also said she sucks her thumb at 6 and I think it's absolutely disgusting and inappropriate, just as inappropriate as her running bottomless after my kid trying to expose herself to him). 

So after the episode my mother in law kept calling every hour to check on my kid and showed up in my house after the baby mama picked up my step daughter. 

My husband is very upset about the incident but he can't do much. 

But after all that the baby mama didn't even have the decency to call or even send me a text apologizing. 

I've been trying really hard for almost 5 years not to hate this bitch but right now I hate her. 

*Edit: I hate the Baby mama. My relationship with my step daughter has always been good. 

Even though her mother is been told to take her to a therapist I don't believe she's a problem child, she's just neglected by her mother who tries to play this split parentes problem thing being that they never even dated (it was a college hookup that got pregnant and threatened to abort, so he let her live in his house till she finished college). 

And the thumb sucking, even her school teachers have been asking us to help her stop because it's harming her schoolperformance but since I'm the one picking her up in school everyday I'm the only one that hears about it directly from her teacher and her mom thinks it's ok.