And she said her email contained language like “and if my demands aren’t met, then I will find an exit date.”

It sounded from her account a straightforward threat to leave.

"We can't meet your demands for sure. But please hang around the company and choose your exit date at your liking" -- no reasonable person would respond like this.

In any case, making this an issue sounds way overkill.

Both want to part way. Either side can choose an earlier date of the termination.

She doesn't need Google's permission to leave earlier. Google also doesn't need her permission to make her leave earlier.