He did it! Jacob named me as Corduroy's secondary caregiver on her medical records! They were able to give me full access to her records. Specifically choosing "Yes" to:
DO YOU AUTHORIZE THE SECONDARY CONTACT LISTED TO MAKE MEDICAL DECISIONS, INCLUDING LIFESAVING AND FINANCIAL DECISIONS, REGARDING YOUR PET IN THE EVENT WE ARE UNABLE TO REACH YOU?
I helped Jacob buy Corduroy because the deal was if he found having a puppy too overwhelming, she'd come live with me. I bought her food, treats, and toys every month OF HER LIFE!
THIS ENTIRE TIME I HAVE BEEN THE ONLY LEGAL GUARDIAN OF CORDUROY! Signed and dated by Jacob himself.
I'm not sure where she was looking for "concrete evidence" but we found it! Sadly, this text was all part of the manipulation I think.