Considering she says she made a list of issues she'd like fixed and that she'd discuss it when she came back from PTO without ever mentioning resignation and that was answered with a "we accept your resignation" passed on to her reports, I believe she has legal representation.

The financial implications of her resigning vs her being fired are probably significant.

In Google's place I'd probably negotiate an agreement with a non-disparagement clause. She'd be compensated and everyone would save face.

And we'd never be discussing this. She could take other research roles and advance the state of AI in peace.