I like the idea of treating her like a toddler and acting like a daycare worker.
"Aunt Bitterhag, it's time to stop complaining about the coffeemaker. If you don't have anything nice to say, don't say anything at all."
"That was not a nice thing to say. In fact, it was quite rude and you owe me an apology. No--apologize now."
"You've made it quite clear that you don't like ham. If you don't like it, don't eat it. But you need to stop whining about it."
But honestly, if it were me, I would make A Scene. I am quiet and nonconfrontational, so if I ever make A Scene, my family knows that I mean business. I have only had to do it once, and I can't tell you how satisfying and effective it was.
A Scene doesn't even have to be rude. Stand tall, put your shoulders back, and say in your best firm voice, "I have had enough. I refuse to be demeaned and abused by Aunt Bitterhag. I am tired of your insults, Aunt, and I refuse to listen to your abuse any longer. You have been unimaginably cruel, and I will not subject myself to your nastiness any longer. [turn to your family] I am sick of you sitting back and making excuses while I am insulted, abused, and driven to tears by a bitter, hateful woman. You have placed her feelings in front of mine for the very last time. I will no longer tolerate this behavior from any of you."
Then leave. Turn off your phone and go do something nice for yourself. Chances are that it will never happen again. If it does, say "I have told you before that I will not subject myself to this abuse." and then leave.