In fact, it's not too late to trick her.
Get her in a private conversation and ask her why she did that. Record the whole thing.
Sorry to hear this. That's a bad situation. I work in an office. I would have berated her in the office with the boss. You are only as good as your word. She made your word look like sh*t. F THAT! The boss would know from my reaction that she was the one lying.
That wouldn't work. She's been there for 10+ years and is a manager. The Boss likes her and promoted her to that position, where she does a lot more than just manage supplies and such.
It doesn't help that Boss was a USMC officer, a helo pilot that was shot down in Vietnam. He doesn't work like your regular manager that team builds. He orders and expects results immediately.
Tough situation. I would have just did what my boss said most likely, but it's tough going against the office manager. They definitely have power trips. He who controls the paper, tape, staples, toner, new chairs, and pens, control the universe!
Still though, if I went your route and after only 7 months I probably would have just sucked it up and took the ass-chewing. In an office you have to carefully choose your battles. Seven months in, you get the ass-chew no harm, no foul, you're new and sh*t happens. In the future, when you're entrenched and established, if you have a "I'll take care of it immediately" attitude, and you're known to take on your responsibilities and lickings, you'll have much more clout for future issues when it really counts. It sounds kiss-ass I know, but office politics are more strategical than chess.
CHOOSE YOUR BATTLES!
Even if the office manager fessed up, your boss would be pissed off that you chose to listen to that person instead of him/her. It was a battle you couldn't win in any circumstance. Take the bullet, jump on the grenade, fall on your sword, when you have to. The respect will come. Now all that happened is your boss thinks you can't do your job, he/she thinks you're a liar, and you made an enemy of the office manager.
The kicker............My new boss.....he's as chauvinist an SOB as you'd ever want to meet.
He actually just put one of the ladies in "charge" of coffee.
And he expects it on his desk first thing.
Drives them crazy......hehe.
If you think for one minute that your boss wouldn't appreciate you standing up for yourself, you are wrong.
Lesson learned.
Office bureaucracy man. Get everything on paper if you can. Instead of discussing something by the water cooler, send her an email instead. That way if shit hits the fan, it's not you who takes the blame.
This is one of the pleasures of working from home, for me. My coworkers and I literally only talk via Skype chat.
I'm one of those guys that is honorable and expect others to be the same. I'm admittedly naiive.
Were I in her shoes; as a manger, I would have supported the employee by admitting that yes, I did say that, and it turns out that it was a mistake that won't happen again. Lesson learned.
But that's me, and I'm a lot better of a person than most people out there in the world.
Whatever. This job is a jumping off point. I have no desire to be there past 1 year. After probation is up, I'm applying at other jurisdictions.