The designer: The London designer has built her reputation dressing the upper echelons of society. And her borderline-prim aesthetic carries serious fashion clout: her “lady” is as chic as they come.   This season it’s about: Inspired by Ali MacGraw (we’re already hooked) tweeds and Ivy League stripes adorn everything from cinched trousers to evening gowns. Our favorite piece? The bib-fronted marigold dress. Perfection.