In California, she doesn't have a lot of fans on either side of the isle.
They aren't. The media are mostly saying that she is both the first Black woman and first Asian (sometimes specifically South Asian) of either gender to be in either slot on a major party Presidential ticket. Which is, entirely, true. Some (though IME a minority; usage has shifted recently) may use “African American” in place of Black, which is also accurate.
> She's Indian and Jamaican
Black people got to Jamaica from the same place (and for the same reason) they got to the rest of the Americas.
> and family owned slaves - doesn't matter to me but it does matter a lot to the current left.
There is very little of the current left to whom it matters that an African American is of mixed race, or that their ancestors were in Jamaica between Africa and the US, or that someone’s distant ancestors owned slaves (which is true, in fact, of quite a lot of the current left, including—perhaps especially, due to the sexual dynamics of chattel slavery in the Americas—Blacks.) Those things tend to be more right-wing distortions of different left-wing positions that the right would rather avoid dealing with head on than significant left-wing positions, though if you tried really hard you could probably find someone on the left who cares about each of those things.
She has substantial opposition on policy issues and past actions in government from some of the left, which isn’t surprising since, like Biden, she's basically a centrist Democrat, though (also like Biden) somewhat more progressive than the center of mass of the centrist neoliberal faction, though. OTOH, it is more the kind of opposition that matters in a primary than a general election.