It's fairly standard to let the employee leave the building immediately but still on payroll for 2 more weeks.
Again, I think it's a non-issue. Both wants to part way. Either party can singlehandedly make that date earlier.
It seems one side brings up this point because other points are not salient, so they try to make it like "you see they fire me today. I actually want to leave in 10 days instead. This is unethical!!". It's a weak point and muddles the main point.
"Effective today" has legal meaning. It's an issue because it shows Google acting in bad faith.
What would be bad is letting a disgruntled employee hanging around company accessing company's material.
And, from what I understand, that she wanted to discuss the issue in person when she returned from vacation (which she was on at the time.)
EDIT: I point this out because I think that this potentially recasts the whole communication from an non-negotiable ultimatum to something more like a fair warning to avoid blindsiding anyone going into an in-person discussion in which negotiation is implicitly anticipated.
Then, she should have said that.
It would be ridiculous for Google to let her hang out at the company.
"Oh we cannot meet your meet ultimatum for sure. But please feel free to hang around and finish your vacation. We'll wait for you, a disgruntled employee, to choose when to leave."
[1] https://twitter.com/timnitGebru/status/1334364736457240577