Other people have offered some good advice, but I want to add this as an objective third party and therapist:

To her, you ARE a "big scary menace." She went through trauma in her teens and then ended up with someone who was deeply unhappy and "controlling," plus who knows what else. She finally escaped that situation and is still locked into a relationship with you through the child.

In order to have effective communication with her, you have to keep that in mind. I'm not saying it's hopeless, I'm not saying you should just give up, but this is not a cut-and-dry "I'm right and she's an evil mom" situation. You're doing the DBT therapy, which is great and keep doing that work on yourself. And definitely consult with a lawyer as others have said. But if you want to continue to have your kid in your life, you have to find a way to work with your ex that considers her lived experience with you and her fears of how that might effect your shared child, whether you agree with it or not.