She wore a LOT of Mr. Cassini in the White House era, but then and throughout her life she wore just about every designer of prominence. She had a shopping addiction and spent hundreds of thousands on clothing every year (and that's not adjusted for inflation) After JFK passed away she would go on mad shopping sprees for distraction, buying things she would never even wear.
During her time as first lady, her lux sartorial choices were criticized as being "too costly" and not very "American" with outrageous amounts listed in tabloids as her yearly wardrobe budget (the figures were closer to truth it was later revealed) to which she famously replied 
"A newspaper reported I spend $30,000 a year buying Paris clothes and that women hate me for it. I couldn’t spend that much unless I wore sable underwear."