Parent called demanding to know exactly how I detected their kid’s plagiarism

Had one of those calls yesterday that leaves you shaking a little after you hang up. Caught a student submitting an essay that was almost word for word a source from a study guide site, easy find, five minutes on Google turned up the original. Gave the student a zero per our academic integrity policy and a meeting was scheduled. The mother called the office directly, skipped me entirely, and demanded the school explain exactly what tool was used, what the percentage match was, and if I had any formal training in plagiarism detection. Principal looped me in on a follow up call today. I walked her through the source comparison side by side and she softened a bit but still pushed on if this was documented enough to survive an appeal. Not my first tough parent conversation but this one felt more adversarial than usual, like she came in ready for a fight. Anyone have a template or process for these calls so I’m not improvising under pressure next time.