I want to insult my cheating ex over the fact her father left her as a child
Why would you insult your ex because of that?
She dissed me and she jeopardizes my relationship by telling lies.
It's okay to be angry at someone who insulted you, but if you insult them back you're just going to escalate the situation. Try finding a way to cool off before confronting them. When you do confront them try to be calm and explain to them why you're upset in a reasonable tone.
I'm filing for a divorce and don't care about any of this.
I think it would be wise to just stop talking to her entirely. It sounds like you two just don't get along.