All of her public statements before and after he dropped out. I don't have time to catalogue them all, but this was just a few days ago:
Pelosi, Obama, and their donor friends they helped organize their pressure campaign with didn't want Harris to be the candidate because they feared (much like a lot of us did as we were discussing the possibility) that she'd be a weaker candidate than Biden (and the donor friends thought she was too progressive). Carville sure as shit didn't want to run a progressive black woman with similar to worse (at the time) favorability numbers than Biden.
I'm as shocked as anyone at how quickly and effectively the party rallied behind Kamala and how quickly she's been able to both increase her popularity and effectively diminish Trump in the public eye. I shared their doubts. But one thing I did know before Biden stepped down is that a contested primary would've been an absolute fucking disaster, and it absolutely would've been, while that whole crew was trying to force Biden to step aside but their entire plan for after that was some underpants gnomes nonsense. Biden and Harris saved us from that insanity and I think we'll likely look back at the 24 hours after Biden announced he wouldn't run as one of the most pivotal moments in American history.