Cooked her in aus meant drugged up or drunk af. You're not the full shilling because of substances, drunk or stoned. It also has just 'crazy' connotations. Even if you're not actually high atm, a schizo could be acting cooked...

Example sentences: "Yo mate I got sooo cooked last night" (after a long night of abusing alcohol and meds) "haha look at Bruce, he's cooked as" (Bruce then gets a cock and/or moustache drawn on his face in a sharpie by Wally)

So then that explains the push to get it associated with antivaxxers.