Previous threads on this ongoing story:
https://news.ycombinator.com/item?id=25292386
https://news.ycombinator.com/item?id=25292386
Also it's likely that her contract allows Google to provide her pay in lieu of her working out the end of her contract, so they are probably able in general to move dates like this (not commenting on the other aspects of this situation though).
Google: "we aren't going to give you x, so you can have y. in fact, you can have y starting right now."
i'd say she tendered a conditional resignation and they called her bluff and accepted it.