No, her being extremist doesn't make it ok to be sexist towards her. Like you should be able to criticise Caitlyn Jenner without being transphobic. Or Milo Yiannopoulos without being homophobic.

Treating her the same as other people who get a lot of non-restorative plastic surgery isn’t right because she isn’t like them.

But making fun of her getting such plastic surgery targets everyone who gets them. Just like making fun of someone for being fat targets every fat person, like calling someone gay as an insults is insulting towards every gay person. I'd argue her being a nazi makes it even less ok since of all the things you could be focusing on you're focusing on something that she fully in her right to do. It makes everything else you say easily dismissable and opens you up to accusation of sexism, because it is sexist to shame and try to humiliate a woman because of how she presents herself in public.

Just like how she is now brushing past all the other criticism south park has of her and focuses on the sexist aspect of her portrayal.