IMHO there were scenarios where she could have won. The timing of when Biden decided to not run / drop out, as you both say, doesn’t figure into those scenarios.
If anything, 107 days might have been about five or six weeks too long. All that seemed to happen between late September and Election Day was Trump-Vance gaining ground.
I think he’d have been a MUCH better choice for VP (Walz was pretty much a dud). If he wasn’t chosen because “ambitious”, that’s on her - a selfish decision.
Weirdly**, for about a month or so, Walz had a lot of juice. He could have been over-exposed, though – it seemed like, after a time, the campaign was forcing the idea that Walz was a “difference maker!”.
If Shapiro actually tried to extract a promise he’d be “co-President”, I’d say she was fully justified in rejecting him. But it’s hard to picture a savvy politician - which he is - saying something that out of line.
I find it more likely he wanted a promise to be treated as a prominent, “front & center” member of her administration, and that she interpreted this as overly ambitious.
There’s also that thing with Shapiro where he quashed the investigation into a friend of his whose wife killed herself by stabbing herself in the back of the head ten times while the husband was home. If Shapiro wants to be a serious candidate, he’s going to have to come up with an explanation for his part in that.
The talk about forming a team of co-presidents between Harris and Shapiro brings to mind the 1980 Republican convention. Ronald Reagan considered asking Gerald Ford to be his running mate on a “dream team”, where they would serve as co-presidents. They couldn’t agree since Reagan didn’t want to give up so much, and of course Reagan would go on to beat Carter without Ford.