I'd call it petty more than sleazy. Drama queens on both sides.
You cannot fire someone for membership in a protected class (race, religion, sexual orientation, etc) or participation in protected activities like reporting an employer’s violations of the law, but it’s difficult to prove intent in such cases.
There are exceptions for unionized workplaces with collective bargaining agreements. Employers in those situations cannot fire employees without “just cause.” Google R&D is not unionized, however.
I assume they wanted her out and she accidentally gave them immunity, so they jumped on it.