Without taking sides (I don't know the full story to understand who is objectively in the wrong here), that's not completely true.
She basically gave an ultimatum - meet my demands or I can work on a last date.[1] It is quite common at big tech that once you resign - officially or unofficially - you could be asked to leave effective immediately. Usually happens when you work in critical areas or moving to a competitor or a disgruntled employee.
Could this have been better handled? Maybe, but no matter who was in the right or wrong, she wasn't technically fired.
[1] https://twitter.com/timnitGebru/status/1334343577044979712