I have no issue with her calling Anti vax people out, she is completely right on that front and that is not the problem here. Where she is in the wrong and what the OP pointed out to her is, that is she got careless and it is ultimately her fault for getting COVID. Not wearing a mask in highly populated areas is foolish and it doesn't matter if you are already vaccinated. She didn't own up to her own mistake and the OP's message clearly hit a nerve. She did not do everything right.
If she didn't want to be "put on the spot" as some people claim she was, then she should have not posted that post on FB, which is public social media platform and the OP was right to comment on it, and no amount of laughable "mind your own business posts" changes this.
So it's okay to victim blame people on social media if they post something publicly. If anti vax people would just get the vaccine then spread would be greatly reduced and there would be less risk. But instead of blaming them, you're gonna blame her for not locking herself in a room for eternity. That's insane