Custody and Visitation Issues: Screenshots As Heresy

My question involves a child custody case from the State of: TX

I'm not sure where to post this, but I am in the middle of an SAPCR. I have screenshots of texts from a friend that prove exactly what I need to prove about my ex, but my attorney says I cannot use them unless we actually subpoena her as a witness, as the screenshots are considered heresy.

I understand that. However, my ex has asked some people to screenshot any messages I send them, and send the screenshots to her. The one who told me that says they will not be appearing in court for either of us.

My questions are: What's the difference in between screenshots of texts between me and her friend about her that I cannot use and screenshots of texts between me and my friend about other random stuff? What's her attorney telling her, or what is she trying to prove? If I can't use my screenshots of a conversation I was directly in; how can she use ones a friend sends to her of a conversation she was not in? How is that even legal evidence if she otherwise had no access to a private conversation?

Custody and Visitation Issues: Screenshots As Heresy