Greedy Landlady

We were renting a room but recently decided to get our own apartment. Today, I informed my landlady that we would only be staying until the end of this month. I even introduced her to a new tenant who would take over the room, ensuring that her income wouldn't be impacted. In short, her rental business would continue without disruption. She agreed to this arrangement but then, out of nowhere, brought up a penalty fee. She claimed that since I gave her short notice, I would need to pay half of the rent as a penalty, even though I've already arranged for another occupant, and they’ve paid a reservation fee.

Initially, I disagreed with her demand, but after a lengthy back-and-forth, I reluctantly agreed just to end the argument. However, I don’t intend to pay her anything because the penalty was never mentioned before. Now, she's threatening to have the building's guards prevent me from moving my belongings out unless I pay. She claims they won't let anyone move out without the landlord’s approval. I suspect this is just a bluff, and even if it’s not, I don’t believe the guards have any legal right to block me.

Is there any legal action I could take if she continues to harass me?