Did you ever try just asking the client what format they wanted before sending the first invoice? I had a similar thing happen with a shop in Austin, except mine was the opposite problem. I used to lump everything into one line that said "services rendered" and a client told me it felt sneaky, like I was hiding something in the total. So now I do what you do, a short summary up top with the full number, then the breakdown underneath. My take is people just want to see the big number first so they know what they owe, then the details are there if they care to look. Funny how the same fix worked for both of us from opposite directions.

Honestly this sounds like one of those things where both sides are kinda right but nobody wants to admit it. The fat does carry flavor, sure, but 80/20 is already pretty greasy and rinsing it for tacos isn't some crime against cooking. Sounds like your aunt just has strong feelings about ground beef, which is fair, but a whole stare-down over it feels like a lot.