I would trust your boss's boss to do the right thing. If your boss is valued, a single incident is not going to be overblown. It is probably a good thing that this person has the entire weekend to consider the incident. Hopefully there isn't anything else hanging over her head right now.
Don't get involved or try to influence the decisions made above your head - especially since you know that the accusation is true. Doing so says that you don't trust the discretion of your boss's boss - not good for your career.
You now know what you have two office rats. I would begin working on cases to have them fired. No way would one of my employees get away with being an office rat. Heck, I'd set them up if I had to.
Be glad that you found out without getting your own back stabbed. People like this do not change. If they stick around, it is only a matter of time before this sort of thing happens again. This is not whistle blowing - this is betrayal.
Once again, I agree with Bama. I've worked in offices where everyone was a team player and bent over backward to get projects in on time, and we also had a great time going out in our off hours and lunches. That is until a rat got hired and started office politics.
Rats destroy productivity, morale and teamwork with their gossip, innuendo and passive/aggressive attitudes. It's been my experience that people who behave like this do it to cover the fact that they're not all that talented to begin with. Their only talent seems to be seeking out the highest ranking member of the company and kissing butt.
People like this leave a paper trail, however. I wouldn't necessarily go out of my way to set them up; I'd merely start with the paper trail already in progress and build on it. If the OP's rat had already enjoyed the boss going to bat for her to keep her even though the company could ill afford to keep her, I think her last rat tactic is about to backfire on her. She obviously misjudged her actions last Friday when she decided to stab that boss in the back by instigating an email "whistleblow" on an activity that had been going on and was overlooked for a long time.
I'm not sure it's a case of "make one's life miserable". From the description, it sounds like she actually went out of her way to "make one's life pleasant." That's a privilege that sounds like it should come to a grinding halt, since it was so obviously not reciprocated.
OP, I abhor a tattletale above almost any other character flaw. Treat the rats like rats.
Agreed.
As for the rats going to HR because I decide to make them do their job instead of sitting around talking on their phones andnot eating lunch with them anymore or buying their tupperware, do you honestly thing HR will give a darn? I am not going to be overtly rude and ugly. I am just switching on the professional persona. This used to be an office where we were all friends, babysat each other's kids, went to tupperware parties for each other, vacation together, etc. Not anymore. If that is how she wants to be it will be a business atmosphere all around. As for getting rid of the one rat who is my assistant, it will be simply a decision based on our numbers. We really can't justify having her any longer. It won't be right away but when it comes up I will just have to act like I am sorry to lose her. I am just so disappointed in her. I thought she was more mature than that.
This is your best action. I doubt seriously that you'll take the tactic of never speaking to her because that's not professional. But taking it to a professional level and holding her accountable for accomplishing her work in a timely manner cannot be judged as unprofessional. My attitude would be "Sorry, but the tupperware party is over. You're here to work, you're getting paid by the hour to do that work, so you'd better be working."
If it were me and I knew how long it takes to complete specific tasks, I'd start setting (reasonable) deadlines. Each time these deadlines were missed I'd be documenting it. I'd probably also start limiting internet time and put a monitor on all hourly employee's computers for the websites visited during business hours. If your numbers already state that the company can't afford two assistants, then the added documentation of how the second assistant doesn't do much anyway will push the decision into the "cut" column.
In all my years of working I've seen great teams destroyed by the introduction of rats and snitches. They nearly always rely on the "I'm just enforcing the business rules" defense and, with investigation, they nearly always turn out to be the worst offenders at not getting anything done.
I wish you the best of luck tomorrow, OP. Keep it professional and stick with the "everyone's here to work, not make friends" attitude until this issue is resolved. You can always try to rebuild the team after the rats have been exterminated. It's difficult to earn the trust the of team members back, and it'll take months or years to do so, but recovering from a rat can be done with patience.