you're engaging again!
She's full of it, you need to say nothing, ignore.
BUT don't be afraid of bring it to ahead if she forces you to acknowledge her comment, you simply deliver a monologue. If she attempts to interrupt you tell her that you've all heard enough of her poison and now it's time to take her medicine.
"You got yourself to the flat and lived, you lugged milk and lived. You still had the energy to snipe and chip away, so clearly you had ample capacity left. You have made it impossible for us to stay a moment longer. I know who and what you are, I know what you were trying to do, and it won't happen. You can turn on the tears, you can write a pack of lies to DB, but bottom line is that he rumbled you before I did."
IF you want any kind of relationship with me and my family going forward, you treat ALL of us with the respect we deserve, or you go home to the UK. You're well able to strop and storm, well able to scheme, manipulate and insult, you can put all of that energy into shopping on or offline, walking and running errands. You did this mum. No-one else, you."
Then you turn and leave.
It's not something there is no way back from, but it's a hard line in the sand. All you do then is repeat the line about your family deserving respect.
Hold HER over an emotional barrel.