If it's that important, and she didn't believe you the first time, you should've requested that she verify the quantity herself. *Sigh*... not that a smart-ass jab like that would help your relationship with that jerk, but having you count thousands of business cards twice at the end of your day just sounds like she's trying to push your buttons.

Sounds like an asshole on a power trip. Did she state why it was so important to count them? Was it part of your job? That honestly sounds like abuse to me.

Next time give her a random odd number like 2798 and she'll never be the wiser!

Maybe you could not count them again, lie and say you did, and say you got 3003 or repeat that you did indeed got 3000. I know lying is awful especially to your boss but she does kind of deserve this. And if she doesn't believe you then tell her she can verify it and count them herself. If she's making you recount them, she probably isn't planning on counting them herself so I think you're safe.

And why exactly would she need an exact number? I'm sure there's more important things. She sounds like a jerk to me.

Wow, and just when you thought she couldn't get more ignorant. She's ridiculous! I hope she paid you for overtime?!

should have counted out a small number, then split the cards into piles the same height then count the piles

Was it after your shift or during? If its during then just do it. If its after then unless she pays you she can't make you do anything. Kindly inform her of your contract, if she chooses to get rid then its unfair dismissal, if she fires you for something else you did then its possibly constructed dismissal.

Was it really 3000?

Aren't there machines for that? And why would she need to know such a thing anyway