She will always have to come to the point of convincing the rank and file that she is the best choice they have.

True, but if there's a vote right now, she will lose. If she waits until after a GE she has all the time between now and then to chip away at Sunak's Gvmt, especially after it loses the GE. There'll be a lot of time to bottle up the party's anger then use it in a leadership bid, time she simply doesn't have now.

I think you're bang on about Cameron. It's a dangerous political move by Sunak for all the reasons you state. I don't think there'll be a flood back exactly but some will return. There's still a huge amount of Johnson fans in the party and a lot may depend on what he thinks of Cameron's return.