Note 1: (aimable) The definition of the French word aimable (according to Larousse's French-English dictionary) is: kind, amiable, pleasant, nice.
The American Heritage Dictionary definition of the English word amiable is: Friendly and agreeable in disposition, good-natured and likable.
The distinction that Knightley seems to be making is the difference between having correct manners and being pleasant to be around.