Despite my user name (I love the character) I would guess my political views are pretty much polar opposites of hers (lefty, anti-death penalty, dislike Trump intensely, do not believe the US election was rigged!)
Having read the antisemitic tweet, I can see you could have two reactions to it. Had she made the same point for instance by invoking the way the Stasi in Communist East Germany got neighbours and children to inform on people (see for instance the "Hate Crimes Bill" currently under discussion in Scotland) I think what she said was fairly unexceptionable - though possibly a bit batshit to compare being monstered on Twitter to being taken off to secret police headquarters in the middle of the night. (Though somehow I doubt she's historically informed enough to make that point - she doesn't strike me as the brightest bulb in the house. However, that in a way is beside the point - in a democracy, everyone gets a voice, even if they're thick, ill-informed, bat-shit, or one group of people who've appointed themselves moral arbiters for society feel their views are "evil.")
The tweet itself was clearly criticising the fact that ordinary people joined in the persecution of Jewish people - not just the SA, Brownshirts, Gestapo. So at no point was she criticising Jewish people; instead the people she was clearly portraying as wrong were the people doing the persecution.
However, it does still leave a nasty taste as a choice of analogy, because the problem with invoking the Holocaust is always that if you use it to say "it starts with [insert fairly trivial point here] and ends with the Holocaust", it's a form of antisemitism because what you are doing is minimising the Holocaust by pressing it into service to support your pretty trivial political point.
Was Disney right to sack her? I suppose Disney has a well-established policy of expecting certain standards of behaviour from their stars (Lindsey Lohan, anyone?), so it's unsurprising. They would see it as reputational/brand damage (though the irony of that from a brand started by a White Supremacist, with a set of deeply racist cartoons among their early output is not lost on me).
I'm disappointed in that I thought she was good in the role, and the character was fantastic.
And yes, there absolutely are double standards. Male stars get away with being rabidly right wing, ragingly, openly antisemitic (thinking of a certain Hollywood A-lister who played Hamlet among other people), openly homophobic, you name it - and no-one bats an eyelid.