In the United States, there is a huge difference legally between being fired and resigning. You don't get to declare someone else's "resignation" for them.
Maybe that's the logical thing, but lots of people also bluff and fail.
I think you are arguing that this is more straightforward than it really is. If we suppose (in absence of her actual email) that she declared "...make x, y, and z happen or I resign", that certainly reads as a (conditional) offer of resignation that can be accepted by the other party.
All of this is likely to end up in court and we'll get a decision on whether it was a resignation or firing.
"However, we believe the end of your employment should happen faster than your email reflects because certain aspects of the email you sent last night to non-management employees in the brain group reflect behavior that is inconsistent with the expectations of a Google manager."
That isn't accepting previously offered conditions. I agree what it means legally will probably end up in court.
[1] https://twitter.com/timnitGebru/status/1334364735446331392
From a legal perspective, she was quite clearly terminated. There was no point at which she "worked on a last date" (her exact words) with her management, they just sent her home.
Now, that said, except for her unemployment eligibility, there's not a lot of legal meaning to "terminated". A later law suit isn't going to be bound by definitions like this.
She did not post the actual email to twitter or elsewhere (nor did she attempt to effectively summarize, oddly). Were you a recipient? If so, please do share (if you're able to legally).
Side note: she is being strangely cryptic about the contents of the email in her tweets.
I am referring, specifically, to the as yet private email exchange between Timnit, Megan(?), and possibly others wherein Timnit offers an ultimatum which Google then declines.
Google terminated her employment sooner and for a different reason than she offered to resign. Firing someone who's offered to resign is still firing.
[1] https://twitter.com/timnitGebru/status/1334364732480958467
In fact, there is no law that states resignation must be submitted in writing (though a contract can stipulate that requirement). I can walk into my boss' office and resign verbally with immediate effect. California is an "at will" state.
That said, I would be happy to read the source you're citing with respect to the employment law relating to resignation if it contradicts my claims.
Totally irrelevant to whether this was a resignation. Your boss can't "resign" you for any reason whatsoever, that is not what "at will" means.
Unless you actually submit your resignation, I don't think they can just "accept" your resignation and that still counts as a firing.