I agree. If you're going to lodge a formal complaint, then pay her. If you're not, then if you don't want to pay, don't. If she bugs you about it, you can threaten to file a complaint since she was negligent by dropping you without at least a referral. Here, if a therapist did that, that's enough to lodge a complaint and get your therapist in some serious trouble.

If you just want to move on, I'd say just pay and leave it in the past. Don't drag it out. I know what it feels like to want to sort of hurt your therapist back, but if you want to move forward, it's going to hinder your progress.