"Nice," "Not Nice," [ModE] and "Nice" [ME / EModE]
In the 1950s, a "nice girl" was sexually chaste and socially demure. "Not nice" girls might have violated social decorum by numerous faults in dress or behavior: wearing clothes with too high a hemline, too low a neckline, too brightly colored; talking too loudly or using "vulgar" language, especially profanity; speaking openly with boys in unchaperoned settings, or accompanying them to private gatherings; being known to be sexually active at some level from kissing to intercourse, or having the rumored reputation of such activity.
Middle English "nice" meant ignorant or foolish, but it also could be used to indicate one was prone to lascivious sexual behavior, depending on context. In this second sense, "nice" came to be a synonym of "wanton." Oddly, "nice" also could mean extravagantly or vulgarly dressed, rather the opposite of American ModE usage. After about 1500, "nice" began to mean concerned with dressing well, strict about details, and finally, by the late 1500s, socially refined and careful in matters of literary taste. Simultaneously, this immensely pliable word also began to be used to mean shy, coy, or reclusive, which is its sense in the title of the mid-sixteenth-century morality play, A Nice Wanton (whose protagonist is both lascivious and shy). In Everyman's c. 1485 Middle Engish, the worldly character, "Kindred," can abandon Everyman while offering him the company of "my maid" who "loveth to go to feasts, there to be nice, / And to dance, and abroad to start," a description whose additional context unambiguously describes her as a sexually loose woman.
No competent user of the language in any of these eras could possibly mistake the meaning of "nice," even though the word completely changed its significance, from (in Middle English usage) a strongly negative code word to target socially active women for shame, to (in American usage) the dominant positive code word for restricting rebellious "not nice" women by targeting them for social shame. For this reason, when learning literatures from other cultures and eras, scholars always look up such words in the O.E.D. or M.E.D. (or in another language's authoritative historical dictionary) to make sure of their denotation and connotation at the time they were used.