I was picking up some things at work today and I heard a coworker talking about me saying I had borrowed some of her things and didnt give them back and didn't want to.

It wasn't true as when I replaced her on the floor she left some stuff behind (mugs, supplies, calendar etc) she said she didn't want it and if I didn't to throw it out. I told her if she ever needed it back, just to come and get it I would keep it for her.

I popped my head in midsentence to ask her a random question so that she knew I had heard what she said, she turned beet red. How do I deal with her at work so that she learns her lesson and respects me?

BTW I returned all of her stuff to her before I left, she wasnt there so I left it on her desk.
Thanks guys, to clarify, I am ok with my boss since I am my bosses assistant and my boss is the floors boss. Second, I dropped her stuff back on her desk so that she didnt have ammo to add anything to her gossip.