Diver should not be blamed for the utter failure of leadership and management by AA, the AOC and Bideau.
The athlete will always believe they can perform. That's a given for the best marathoners in the world. It's management's role to step in amd protect them from themselves.
Athletics Australia can and do have very specific fitness tests.
For example before Tokyo, Cedric Dubler pulled his hamstring. AA/AOC required him to run at 95% max velocity for 30 metres and show strong block starts before letting him compete.
He documented it all very transparently in link below (at time 20.49).
I would bet good money Bideau made sure Diver didn't have to do something similar (maybe 80k ran for the week, 6x1k at marathon pace) a week to ten days out.
If she had passed an appropriate test - they could have put it out there immediately after she dropped out, sensible runners would have said 'fair enough' and that would have been that. There would have been criticism but it wouldn't have been legit.
AA/AOC have hung their athletes out to dry from the very start with their policy failure then arrogant statement around selection. They are a shambles and a disgrace.