I've listened to several of her interviews and I get the impression that, given that the MAGA-verse hates her, she is hesitant to endorse anyone because it could actually be counterproductive for candidates who are attempting to woo not-yet-completely-batshit-crazy Trump supporters. I wouldn't be surprised if she eventually announces she's voting for Biden (or maybe she will say 'against Trump'?) just before the election. It makes sense because that would also make a bigger splash.