Stupid woman!

If DD had been feeling stroppy, she could have replied equally loudly. "Thank you so much, you are very generous to share with us every germ, bacterium and virus you have when they spray out as you tell us that. Are you planning to share anything more useful, like the supplies of hard-to-find items you have been stockpiling?"

She sounds like the kind of woman who has bought up trolleyfuls of the things everyone else needs, because she thinks only of herself, not of anyone else. If she declares that she hasn't, DD can reply that it would be axactly the action of someone too selfish to block any coughs and sneezes - or even loud speech - with a mask.