Heather refers to the girls who Pullings photographed as "tarts". An American would normally not use "tart" which is British colloquialism, but people living in a community for a period of time do begin to use local expressions especially when being ingratiating. Further, the opposite is normally true, in that British drama is skewed to use American colloquialism, even when inappropriate, presumably so that US TV buyers will not assume their viewers won't understand what's being said.