and possibly capable of kicking ass
There's no possibly. You already did. You left. That's biggest ass kicking you could give and the best lesson to your child.
I'm sorry you had to live through such terror.
To Op, it does come in stages, first you don't notice it, then by the time you do, it's too late, you're already broken by them. It might take days, weeks or even years for to move beyond 'too beaten down to care' stage. And then comes anger. This is when you start planning to leave, this is where you are now, it comes with healthy dollop of fear. Ignore that, harness the anger, you are worth more, you deserve better. Do whatever it takes, no matter how terrifying to secure your freedom.
Next comes grief. It starts when you leave or when your exit plan is cleat. Don't panic about that, don't question yourself, it's normal. It doesn't mean you did the wrong thing, only that you mourn for what could have been, what was 'meant' to have been. Ignore that too. It would never have been. You would have been trapped forever. Abuse lies, it shows you what you want most to tie you down and delivers something entirely different.
Finally we reach acceptance and healing. This is the good bit, aim for this stage, it takes a while to get here, you might think you're here a few times during the anger and mourning stages and then bounce back. Don't worry, that's normal. Keep going. You'll get there. You are worth it.
Good luck.
Oh and FWIW I heard my abusive Ex-h left me today. I laughed, and I laughed and I laughed. It's almost as funny as the time he promised I could go back to him, if only I'd agree to be a good girl.
Asshole.