When you see her next and she is quiet and putting on a wow is me how (basically waiting for you to ask what is wrong so she can have a go) ignore and talk about the weather, the high street, something on the news, the cost of petrol, a book you read and she should too, a TV programme. And on and on. You don't have to talk about anything meaningful.
If she asks a question, tell her it is all fine and then bring up the high street shop you saw being opened and want to try.
I trick I use is, I go in with a time I have to leave. 'Hi mum. Just so you know we need to leave by 12 as I need to pick up a friends child from somewhere ' remember, this doesn't have to be true, but gives you an out at a reasonable time.
If she starts in on you. Don't defend yourself. Just say, 'this conversation was over last week, it doesn't matter now and you don't want to relive it. Have you read this book by such and such?'
If she tries again 'sorry mum, had already said I don't want to discuss it again. Did you see the new Dr Who?'
' look mum, if it really upset you that much, we will leave. Now dos you see the price of petrol?'
'Ok mum. We are going. Kids get your stuff, grandma is not up for visitors today.'
Put you own spin on it, but may help.
Then start not answering the phone and. Or being able to visit.