Why, because she’s not wearing a micro bikini or skin tight leotard to show off everything? Any anthro element about her must necessarily be modeled after her mistress’s lifestyle, and she was as traditional an English High born Lady as you could get from the lower nobility. Ergo, Duchess will DRESS like an actual “duchess” of 1960s England, who would do nothing the Queen’s family wouldn’t do. Of course, NOWADAYS they have an American born Duchess who has done that, but this is about period accuracy.