AOC is already too tainted by Republican smears and her self-description as a socialist.
Republicans will "taint" any leftist they can as a socialist, even moreso if they have youth appeal and/or are female and/or are not white. Based on your advice, Democrats can never nominate a leftist candidate because the GOP will definitely convince the public that they are socialists or communists, so don't even try.
Dems are not going to allow the GOP to basically shape their party for them. If (massive massive if) the Democrats want to nominate a leftist, that's what they'll do.