The fact that she's still a Dem detracts from/cancels out her good qualities as an individual politician. She implicitly promotes Dem entryism and tailing the neoliberal Dems by staying in the Democratic Party, which is a capitalist party "through and through", to paraphrase Pelosi. There's an actual systemic materialist basis for criticizing AOC and by extension the rest of the Squad and DSA Dems; any individual instance of AOC falling short is a symptom of this broader problem.