The biggest criticism leveled at her so far has been her record as an Attorney General for California, where she was actually very aggressive as a prosecutor, and often took an approach to it that I wouldn't really call 'progressive' (soft paywall):

https://www.nytimes.com/2019/01/17/opinion/kamala-harris-criminal-justice.html

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This has made her somewhat divisive among black communities, as a candidate. She has attempted to respond, but whether her response is good enough is really up to you. She's gotten a lot of 'two-face' comments, which are hard to separate from sexist criticism, and people are already drawing similarities to Hillary (possibly also for sexist reasons).

https://www.vox.com/2019/1/21/18191864/kamala-harris-2020-criminal-justice