It's a sad and terrible truth that sometimes people who were abused will become abusers themselves. I will not excuse her actions as she is a grown woman and has no excuse for her actions but I do pity her because I've seen this before, far to many times.
I have friends who were abusers and many of them took the time to better themselves and they did it. They stopped being terrible people and are now often amazing, one of them even got to be the best man to his ex's wedding. But I've also known people who refuse to change and are still as horrible as they were were. Maybe they didn't start that way but it's who they are now.
I can only hope that one day Rowling realizes what she has become and works to better herself and see that she is as awful as those she claims to hate. I'm not holding my breath and I have no interest in helping someone who refuses to see what they have become.
Sometimes, people are to broken for us to help.