I think a number of people have mentioned it but I don't think Google let her go because of either her email or paper. Her email alludes to there being tensions already present between her and her superiors for at least a year. It sounds like they may have already tried to have let her go. However, legally, they could not.

This latest event gave them an opportunity, since, she essentially gave them an ultimatum. Perhaps after last year's legal success she felt she would have the upper-hand and didn't expect them to actually decline her conditions.

Honestly, the focus on the paper is coming more from her and her supporters trying to spin it (although I'm sure many truly believe it) to make it sound like she was fired for trying to uncover ethical flaws at Google. When in reality, it sounds like she was difficult to work with and burnt a lot of bridges